If you're seeing this message, it means we're having trouble loading external resources on our website. Show
If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. Hurricanes Frequently Asked Questions(Revised June 1, 2021)Hurricane Season InformationHurricane Awareness week runs from May 25th through May 31st and is a great time to get your hurricane kit and plans up to date. The Atlantic hurricane season is June 1st to November 30th. In the East Pacific, it runs from May 15th to November 30th. For more information: When is Hurricane Season? NOAA’s seasonal outlook is published here: NOAA Seasonal Outlook The Saffir-Simpson ScaleThe Saffir-Simpson Scale classifies hurricane-strength tropical cyclones into five categories (1-5) based on maximum sustained wind speed. Major hurricanes (also called intense hurricanes) fall into categories 3, 4, and 5 on the Saffir-Simpson Scale. A super-typhoon reaches category 4 or 5 on the Saffir-Simpson Scale. Jump to FAQ HeadersDefinitions & Storm NamesWhat Is a Tropical Cyclone, Tropical Disturbance, Tropical Depression, Tropical Storm, Hurricane, and Typhoon?A tropical cyclone is a generic term for a low-pressure system that formed over tropical waters (25°S to 25°N) with thunderstorm activity near the center of its closed, cyclonic winds. Tropical cyclones derive their energy from vertical temperature differences, are symmetrical, and have a warm core. If it lacks a closed circulation it is called a tropical disturbance. If it has a closed circulation but under 39 mph (34 knots, or 17 meters per second) maximum sustained surface winds, it is called a tropical depression. When winds exceed that threshold, it becomes a tropical storm and is given a name. Once winds exceed 74 mph (64 knots, 33 meters per second) it will be designated a hurricane (in the Atlantic or East Pacific Oceans) or a typhoon (in the northern West Pacific). Tropical Disturbances -> Tropical Depressions -> Tropical Storms -> Hurricane or Typhoon. References: Holland, G.J. (1993): “Ready Reckoner” – Chapter 9, Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland Neumann, C.J. (1993): “Global Overview” – Chapter 1″ Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland What Is the Difference Between a Sub-tropical Cyclone, an Extra-tropical Cyclone, and a Post-tropical Cyclone?The “sub-tropical” in sub-tropical cyclone refers to the latitudes 25°N to 35°N (or °S). However, the term refers to cyclones whose characteristics are neither fully tropical nor extratropical. They are either asymmetrical with a warm core or symmetrical with a cold core. Sub-tropical cyclones can transform into tropical or extra-tropical storms depending on conditions. The “extra-tropical” in extra-tropical cyclone refers to the latitudes 35°N to 65°N (or °S). However, the term refers to cyclones that get their energy from the horizontal temperature contrasts that exist in the atmosphere. Extra-tropical cyclones are low-pressure systems generally associated with cold fronts, warm fronts, and occluded fronts. They are asymmetrical and have a cold core. A post-tropical cyclone is a former tropical cyclone that no longer possesses sufficient characteristics to be considered a tropical cyclone, such as convection at its center. Post-tropical cyclones can continue producing heavy rains and high winds. Former tropical cyclones that have become fully extra-tropical, sub-tropical, or remnant lows, are three classes of post-tropical cyclones. Neutercane is a term no longer in use. It referred to small (<100 miles in diameter) sub-tropical low-pressure systems that are short-lived. Why are forecast times referred to as UTC or GMT?If you’re wondering, “what is UTC time?”, or “what is GMT time?”, or “What is Z time?”, the answer is they are time schemes. Universal Time Coordinated (UTC) used to be Greenwich Mean Time and Zulu Time (Z). This is the time at the Prime Meridian given in hours and minutes on a 24 hour clock. Most satellite pictures will give the time code next to the time taken with a UTC, GMT, or Z, but they are the same time zone. The conversion table for local times can be found below. On most satellite pictures and radar images the time will be given. If it’s not in local time then it will usually be given as UTC, GMT, or Z time. To convert this to your local time it is necessary to subtract the appropriate number of hours for the Western Hemisphere or add the correct number of hours for the Eastern Hemisphere. And don’t forget the extra hour adjustment for Daylight Savings Time or Winter Time over Standard Time for your zone.
What Are the CDO and TUTT?Central Dense Overcast (CDO) – This is the cirrus cloud shield that results from the thunderstorms in the eyewall of a tropical cyclone and its rainbands. Before the tropical cyclone reaches hurricane strength (33 m/s, 64 kts, 74mph), typically the CDO is uniformly showing the cold cloud tops of the cirrus with no eye apparent. Once the storm reaches the hurricane strength threshold, usually an eye can be seen in either the infrared or visible channels of the satellites. Tropical cyclones that have nearly circular CDO’s are indicative of favorable, low vertical shear environments. Tropical Upper Tropospheric Trough- A “TUTT” is a Tropical Upper Tropospheric Trough. A TUTT low is a TUTT that has completely cut-off. TUTT lows are more commonly known in the Western Hemisphere as an “upper cold low”. TUTTs are different than mid-latitude troughs in that they are maintained by subsidence warming near the tropopause which balances radiational cooling. TUTTs are important for tropical cyclone forecasting as they can force large amounts of vertical wind shear over tropical disturbances and tropical cyclones which may inhibit their strengthening. There are also suggestions that TUTTs can assist tropical cyclone genesis and intensification by providing additional forced ascent near the storm center and/or by allowing for an efficient outflow channel in the upper troposphere. How Are Hurricanes Named?Prior to the 20th century, hurricane names were inspired by everything from saints’ feast days, ship names, to unpopular politicians. In 1950, the National Hurricane Center officially began designating Atlantic hurricanes with code names and then women’s names. In 1979, naming responsibility was passed to a committee of the World Meteorological Organization who used alternating men and women’s names following the practice adopted by Australia’s Bureau of Meteorology three years earlier in 1975. Currently, there are six yearly lists used in rotation found here. If a particularly damaging storm occurs, the name of that storm is retired. Storms retired in 2017 include Harvey, Irma, Maria, and Nate. If there are more storms than names on the list in a given season, an auxiliary name list is used. Lastly, if a storm happens to move across basins, it keeps the original name. The only time it is renamed is in the case that it dissipates to a tropical disturbance and then reforms. In the Atlantic basin, tropical cyclone names are “retired” (not to be used again for a new storm) if it is deemed to be quite noteworthy because of the damage and/or deaths it caused. This is to prevent confusion with a historically well-known cyclone with a current one in the Atlantic basin. Sometimes names are removed for other reasons, such as cultural considerations or politics. History of Hurricane NamingFor much of history, tropical cyclones were only given designations post facto. After they had come ashore and done much destruction, they would be commemorated by being named either for the Saint’s feast day they happened on (such as the San Felipe hurricanes in 1876 & 1928) or by some characteristic (the Salty hurricane 1810, the Yankee hurricane 1935). The first use of a proper name for a tropical cyclone was by Clement Wragge, an Australian forecaster late in the 19th century. He first designated tropical cyclones by the letters of the Greek alphabet, then started using South Sea Island girls’ names. When the newly constituted Australian national government failed to create a federal weather bureau and appoint him director, Wragge began naming cyclones “after political figures whom he disliked. By properly naming a hurricane, the weatherman could publicly describe a politician (who perhaps was not too generous with weather-bureau appropriations) as ‘causing great distress’ or ‘wandering aimlessly about the Pacific.’ “Dunn and Miller (1960). Although Wragge’s naming practice lapsed when his Queensland weather bureau closed in 1903, forty years later the idea inspired author George R. Stewart. In his 1941 novel “Storm”, a junior meteorologist named Pacific extratropical storms after former girlfriends. The novel was widely read, especially by US Army Air Forces and Navy meteorologists during World War II. When Reid Bryson, E.B. Buxton, and Bill Plumley were assigned to a USAAF base on Saipan in 1944 they had to forecast any tropical cyclones affecting operations. They decided (à la Stewart) to name them after their wives. In 1945, the armed services publicly adopted a list of women’s names for typhoons of the western Pacific using the names of officers’ wives assigned to forward forecast centers on Guam and the Philippines. However, the Air Forces were unable to persuade the U.S. Weather Bureau (USWB) to adopt a similar practice for Atlantic hurricanes. Starting in 1947, the Air Force Hurricane Office in Miami began designating tropical cyclones of the North Atlantic Ocean using the Army/Navy phonetic alphabet (Able-Baker-Charlie-etc.) in internal communications. During the busy 1950 hurricane season there were three hurricanes occurring simultaneously in the Atlantic basin, causing considerable confusion. Grady Norton of the USWB’s Miami Hurricane Warning Center then decided to use the Air Force’s naming system in public bulletins and in his year-end summary. By the next year, these names began appearing in newspaper articles. This practice proved popular. However, in 1952 a new International phonetic alphabet was adopted (Alpha-Beta-Charlie-etc.) which caused some confusion about which names were to be used. So in 1953, the US Weather Bureau finally acceded to the Armed Services’ practice of using women’s names. This was both controversial and popular. In 1978, under political pressure, the US National Hurricane Center (NHC) requested that the WMO’s Region IV Hurricane Committee (which had just taken control of the list) switch to a hurricane name list that alternated men’s and women’s names following the practice adopted by Australia’s Bureau of Meteorology in 1975. This was first implemented in the eastern Pacific then in 1979 in the Atlantic. A rare hurricane near Hawaii in 1950 was called Hiki (Hawai’ian for Able). In 1957, three storms were detected in the Central Pacific, and the military forecast centers called them Kanoa, Della and Nina. In 1959, another hurricane threatened the islands and the Weather Bureau designated it “Dot”. The next year an official name list for tropical cyclones was drawn up for the Northeast Pacific basin. In 1978, both men’s and women’s names were utilized, and in 1979 a separate list was created for the Central Pacific (from 140°W to 180°W) using Hawaiian names. The Northwest Pacific basin tropical cyclones were given women’s names officially starting in 1945 and men’s names were also included beginning in 1979. As of 1 January 2000, tropical cyclones in the Northwest Pacific basin are now being named from a new and very different list. The new names contributed by all the nations and territories that are members of the WMO’s Typhoon Committee. These newly selected names have two major differences from the rest of the world’s tropical cyclone name rosters.
The Philippine weather service PAGASA maintains their own separate list of names for any tropical system that threatens their archipelago. For many years the Indian Ocean cyclones were given alphanumeric designators. The Southwest Indian Ocean tropical cyclones were first named during the 1960/1961 season. The North Indian Ocean region tropical cyclones were named as of 2006. The Australian and South Pacific region (east of 90E, south of the equator) started giving women’s names to the storms for the 1964/1965 season and both men’s and women’s names for the 1974/1975 season. For the 2008/2009 season the three separate name lists of the different BoM forecast centers were consolidated into one list. A rare South Atlantic storm in 2004 was post facto given the name Catarina. Another such system in 2010 was designated Anita after the fact. Starting in 2011, a name list was begun for the South Atlantic basin using mostly Brazilian designations. Reference: Dunn, G.E. and B.I. Miller (1960): Atlantic Hurricanes, Louisiana State Univ. Press, Baton Rouge, Louisiana, 377pp Skilton, Liz, (2019): Tempest, Louisiana State Univ. Press, Baton Rouge, Louisiana, 306pp What Happens if You Run out of Names on the List?Well, we all found out the answer in 2005 and 2020. In those years, when they ran through the name list they then use the Greek alphabet : Alpha, Beta, Gamma, Delta, Epsilon,… etc. . In 2020, they made it to a Iota on the list. Since several Greek-letter storms that year were damaging enough to have their names retired, it was decided to scrap this scheme and instead come up with an auxiliary name list each year. The same was done for the East Pacific name lists. In the Central and West Pacific they have a perpetual lists of names, so when one list is through they simply start on the next. How do I Nominate a Name for the Hurricane Name List?Since 1978, the United Nations’ World Meteorological Organization, a group representing some 120 different countries, has used pre-determined lists of names for tropical storms for each ocean basin of the world. The Atlantic basin, which falls under Regional Association IV, has a six year supply of names with 21 names for each year. Why 21 names? Well, the letters Q, U, X, Y and Z are not used because names beginning with those letters are in short supply (you would need at least 3 male and 3 female names for each letter, plus a backup supply for those retired). Think about it; how many men and women do you know whose names begin with these letters? When a damage or casualty producing storm like Mitch, Andrew, or Katrina strikes, the country most affected by the storm may recommend to the World Meteorological Organization’s Regional Association that the name be “retired.” Retiring a name is an act of respect for its victims, and reduces confusion in the insurance, legal or scientific literature. A retired name is replaced with a like-gender name beginning with the same letter. For example, Honduras recommended (1998) the name Mitch be retired and proposed the replacement name, Matthew, for consideration (and vote) by the 25-member countries of the Regional Association-IV. Eighty-three names have been retired in the Atlantic basin. The names used on the list must meet some fundamental criteria. They should be short, and readily understood when broadcast. Further the names must be culturally sensitive and not convey some unintended and potentially inflammatory meaning. The potential for misunderstanding increases when you figure that in the Atlantic basin there are twenty-four countries, reflecting an international mix of English, Spanish and French cultures. Typically, over the historical record, about one storm each year causes so much death and destruction that its name is considered for retirement. This means that in a “normal” year, the odds are about 1 in 8 of requiring a replacement name, given that over the last 57 years (of reliable record) we’ve averaged slightly over 8 tropical storms and hurricanes per season (actually 8.6). So, it’s more likely that letters/ names toward the front of the alphabet (letters A through H) might be retired. The Region IV Naming Committee has a rather large file folder of nominated names that have already been submitted. The next time the need arises and it’s a storm affecting mainly the United States, the Committee will be casting about for a replacement tropical cyclone name. They will take out this file to make a selection. But as we say, it’s pure chance from there. What Are Those Alphanumeric Designations Associated with Hurricanes?The Automated Tropical Cyclone Forecast (ATCF) system was developed for the Joint Typhoon Warning Center in 1988. It is used by computer software to identify tropical cyclones and assist in the generation of forecast messages. In order to distinguish different tropical cyclones that might be occurring simultaneously, a distinct alphanumeric code is assigned to each cyclone once it develops a closed circulation. This code system was adopted by other warning centers in order to facilitate the passing of storm information and reduce confusion. The code designation consists of two letters designating the oceanic basin (“AL” for Atlantic, “EP” for Eastern Pacific, “CP” for Central Pacific and “WP” for Western Pacific), a two-digit number designating the sequential number of that particular cyclone for that basin in the year, and lastly a four-digit year number. So, the first depression to form in the Atlantic for 2001 would be AL012001, the third depression for the Central Pacific in 1999 would be CP031999. A cyclone retains its ATCF code designation as long as it remains a distinct tropical vortex. Even if it becomes a named tropical storm or hurricane the software will still track it by its ATCF code. AL90, AL92, 92L from the Tropical Discussions Oftentimes, hurricane specialists become curious about disturbances in the tropics long before they form into tropical depressions and are given a tropical cyclone number. In order to alert forecasting centers that they are investigating such a disturbance and that they wish to have it tracked by the various forecast models, the specialist will attach a 9-series number to it. The first such disturbance of the year will be designated 90, the next 91, and so on until 99. After that, they restart the sequence with 90 again. The purpose of these numbers is to clarify which disturbance they are tracking as there are often more than one happening at the same time. To further clarify matters, each number is accompanied by a two-letter code designating which tropical cyclone basin the disturbance is in. “AL” is used for the Atlantic basin (including the Caribbean Sea and Gulf of Mexico), “EP” for the Eastern Pacific, “CP” for Central Pacific, and “WP” for the Western Pacific. In discussions, these designations will be shortened to 90L, 91L, and so forth. They may also be referred to as ‘Invest 90L’. However, once a disturbance is designated a tropical depression this 9-series number will be dropped and an ATCF code number will be assigned in its place. You may also occasionally see an 8-series number, such as AL82. This means that this is a test investigation. There is no particular disturbance that the specialists are interested in, they’re just running a test of the system to make sure communications and software are running properly.
Which Hurricane Names have been Retired?In the Atlantic basin, tropical cyclone names are “retired” (not to be used again for a new storm) if it is deemed to be quite noteworthy because of the damage and/or deaths it caused. This is to prevent confusion with a historically well-known cyclone and a current one in the Atlantic basin. Sometimes names are removed for other reasons, such as cultural considerations or politics. The following list gives the names that have been retired and the year of the storm in question. Retired hurricane namesAtlantic
Name retired because of previous storm in 1954 with the same name. Although rarer, some East Pacific names have been retired from the list. The climatology of this basin has most hurricanes moving away from the shore, so chances are rare that these storms would adversely affect people necessitating the name be retired. Retired hurricane namesEast Pacific
Name retired because of political or social considerations A few Central Pacific names have been retired from their list. Most of them were removed for inflicting damage or adversely affecting the Hawaiian Islands. However, some have moved into the western Pacific to cause destructions, prompting their retirement. Retired hurricane namesCentral Pacific
Names retired before the 2000 season come from the name lists used by the Joint Typhoon Warning Center. Since 2000, the names removed come from the name lists used by the Japan Meteorological Agency. Most of the retired names inflicted significant damage to the nations affected. Retired typhoon namesWestern Pacific
Bess 1974 was retired after the season and replaced with Bonnie. In 1979, new name lists featuring both sexes were introduced and Bess was added back. In 1982, Bess was again retired and replaced with Brenda. What Is the Origin of the Word "Hurricane"?HURRICANE was derived from the name of the Mayan god ‘Hurakan’, one of their creator gods, who blew his breath across the chaotic water and brought forth dry land. Later he destroyed the men of wood with a great storm and flood. Through trade Mayan religious beliefs spread throughout the Caribbean. When Columbus met the Taino tribe on Hispañola, they told him about ‘Hurican’, an evil god of storms. Spanish sailors began to refer to these tropical storms by the name of the Taino storm god. Throughout history there have been many alternative spellings in different languages: foracan, foracane, furacana, furacane, furicane, furicano, haracana, harauncana, haraucane, haroucana, harrycain, hauracane, haurachana, herican, hericane, hericano, herocane, herricao, herycano, heuricane, hiracano, hirecano, hurac[s]n,
huracano, hurican, hurleblast, hurlecan, Anatomy and Life Cycle of a HurricaneHow Do Tropical Cyclones Form?In order for a tropical cyclone to form, several atmospheric and marine conditions must be met. Temperature & Humidity: Ocean waters should be 80° Fahrenheit at the surface and warm for a depth of 150 feet, because warm ocean waters fuel the heat engines of tropical cyclones. They also need an atmosphere which cools fast enough with increasing height so that the difference between the top and bottom of the atmosphere can create thunderstorm conditions. A moist mid-troposphere (3 miles high) is also needed because dry air ingested into thunderstorms at mid-level can kill the circulation. Spin & Location: The Coriolis force is an apparent force that deflects movement to the right coming from the Northern hemisphere and to the left coming from the Southern hemisphere. The force is greatest at the poles and zero at the equator, so the storm must be at least 300 miles from the equator in order for the Coriolis force to create the spin. This force causes hurricanes in the Northern hemisphere to rotate counter-clockwise, and in the southern hemisphere to rotate clockwise. This spin may play some role in helping tropical cyclones to organize. (As a side note: the Coriolis force is not strong enough to affect small containers such as in sinks and toilets. The notion that the water flushes the other way in the opposite hemisphere is a myth.) Wind: Low vertical wind shear (the change of wind speed and direction with height) between the surface and the upper troposphere favors the thunderstorm formation, which provides the energy for tropical cyclones. Too much wind shear will disrupt or weaken the convection. Having these conditions met is necessary but not sufficient, as many disturbances that appear to have favorable conditions do not develop. Past work (Velasco and Fritsch 1987, Chen and Frank 1993, Emanuel 1993) has identified that large thunderstorm systems (called mesoscale convective complexes) often produce an inertially stable, warm core vortex in the trailing altostratus decks of the MCC. These mesovortices have a horizontal scale of approximately 100 to 200 km [75 to 150 mi], are strongest in the mid-troposphere (5 km [3 mi]) and have no appreciable signature at the surface. Zehr (1992) hypothesizes that genesis of the tropical cyclones occurs in two stages: stage 1 occurs when the called mesoscale convective complex produces a mesoscale vortex. Stage 2 occurs when a second blow up of convection at the mesoscale vortex initiates the intensification process of lowering central pressure and increasing swirling winds. References: Graham, N. E., and T. P. Barnett, 1987: Sea surface temperature, surface wind divergence, and convection over tropical oceans. Science, No.238, pp. 657-659. Gray, W.M. (1968): “A global view of the origin of tropical disturbances and storms” Mon. Wea. Rev., 96, pp.669-700 Gray, W.M. (1979): “Hurricanes: Their formation, structure and likely role in the tropical circulation” Meteorology Over Tropical Oceans. D. B. Shaw (Ed.), Roy. Meteor. Soc., James Glaisher House, Grenville Place, Bracknell, Berkshire, RG12 1BX, pp.155-218 Chen, S.A., and W.M. Frank (1993): “A numerical study of the genesis of extratropical convective mesovortices. Part I: Evolution and dynamics” J. Atmos. Sci., 50, pp.2401-2426 Emanuel, K.A. (1993): “The physics of tropical cyclogenesis over the Eastern Pacific. Tropical Cyclone Disasters J. Lighthill, Z. Zhemin, G. J. Holland, K. Emanuel (Eds.), Peking University Press, Beijing, 136-142 Palmen, E. H., 1948: On the formation and structure of tropical cyclones. Geophysica , Univ. of Helsinki, Vol. 3, 1948, pp. 26-38. Velasco, I., and J.M. Fritsch (1987): “Mesoscale convective complexes in the Americas” J. Geophys. Res., 92, pp.9561-9613 Zehr, R.M. (1992): “Tropical cyclogenesis in the western North Pacific. NOAA Technical Report NESDIS 61, U. S. Department of Commerce, Washington, DC 20233, 181 pp. What Causes Tropical Cyclones and What Affects Their Formation?In addition to hurricane-favorable conditions such as temperature and humidity, many repeating atmospheric phenomenon contribute to causing and intensifying tropical cyclones. For example, African Easterly Waves (AEW) are winds in the lower troposphere (ocean surface to 3 miles above) that originate and travel from Africa at speeds of about 3-mph westward as a result of the African Easterly Jet. These winds are seen from April until November. About 85% of intense hurricanes and about 60% of smaller storms have their origin in African Easterly Waves. The Saharan Air Layer (SAL) is another significant seeding phenomenon affecting tropical storms. It is a mass of dry, mineral-rich, dusty air that forms over the Sahara from late spring to early fall and moves over the tropical North Atlantic every 3-5 days at speeds of 22-55mph (10-25 meters per second). These air masses are 1-2 miles deep and exist in the lower troposphere. They can be as wide as the continental US and have significant moderating impacts on tropical cyclone intensity and formation because the dry, intense air can deprive the storm of moisture and wind shear can interfere with its convection. However, disturbances on the periphery of the Saharan Air Layer can receive a boost in their convection and spin. An upper atmospheric perturbation known as the Madden-Julian Oscillation (MJO) can travel around the globe on a time-scale of weeks. As its positive phase passes over an area it can bring favorable conditions for convection, while its negative phase can suppress it. This can affect forming tropical cyclones either giving them a boost or hindering them. The climatic fluctuation in the Pacific Ocean known as the El Niño-Southern Oscillation (ENSO) can affect Atlantic tropical cyclone development by increasing or decreasing (depending on ENSO phase) the vertical wind shear over the western side of the basin. The Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO) are oceanic temperature fluctuations occurring over tens of years. They can have a profound influence on the overall tropical cyclone activity over the world’s tropical oceans. For example, when the tropical North Atlantic Ocean is warmer than usual, hurricanes tend to form more often and become stronger. See more in the Tropical Cyclone Climatology Section on Atlantic Multi-decadal Variability. Cape Verde-type hurricanes are Atlantic basin tropical cyclones that develop into tropical storms fairly close (<1000 km [600 mi] or so) to the Cape Verde Islands and then become hurricanes before reaching the Caribbean. Typically, this may occur in August and September, but in rare years (like 1995) this may occur in late July and/or early October. The numbers range from none to around five per year – with an average of 2 per year. References: Dunn, G. E., 1940: “Cyclogenesis in the tropical Atlantic” Bull. Amer. Meteor. Soc., 21, pp.215-229 Riehl, H., 1945: “Waves in the easterlies and the polar front in the tropics” Misc. Rep. No. 17, Department of Meteorology, University of Chicago, 79 pp. Burpee, R. W., (1972): “The origin and structure of easterly waves in the lower troposphere of North Africa” J. Atmos. Sci., 29, pp.77-90 Burpee, R. W., (1974): “Characteristics of the North African easterly waves during the summers of 1968 and 1969” J. Atmos. Sci., 31, pp.1556-1570 Landsea, C.W. (1993): “A climatology of intense (or major) Atlantic hurricanes” Mon. Wea. Rev., 121, pp.1703-1713 Avila, L. A., and R. J. Pasch, 1995: “Atlantic tropical systems of 1993” Mon. Wea. Rev., 123, pp.887-896
What Is the Life Cycle of a Hurricane and How Do They Move?When a tropical disturbance organizes into a tropical depression, the thunderstorms will begin to line up in spiral bands along the inflowing wind. The winds will begin to increase, and eventually the inner bands will close off into an eyewall, surrounding a central calm area known as the eye. This usually happens around the time wind speeds reach hurricane force. When the hurricane reaches its mature stage, eyewall replacement cycles may begin. Each cycle will be accompanied by fluctuations in the strength of the storm. Peak winds may diminish when a new eyewall replaces the old, but then re-strengthen as the new eyewall becomes established. If the storm passes through an area of high vertical wind shear or dry air the storm could be weakened. However, if it continues to pick up moisture from a warm environment, then it could become a major hurricane. Hurricanes are driven by larger scale circulation patterns. The predominant pattern in the tropics is the Subtropical ridge, a semi-permanent high pressure cell roughly located near the Tropic of Cancer or Capricorn (23°26′ N or S). In the Atlantic this ridge is often called the Bermuda High due to its location. South of the ridge the circulation drives tropical cyclones westward with a slight poleward component. But when the cyclone reaches the westward edge of the ridge it will tend to move around the high first poleward then easterly. This is known as recurvature. This motion means that many Atlantic hurricanes may recurve back out to sea without ever making landfall. If a hurricane reaches the mid-latitudes, it can interact with fronts. Often the energy and moisture of tropical cyclones will be absorbed into such fronts, transitioning into extratropical low pressure storms. Studies have shown that this process can increase the unpredictability of mid-latitude weather downstream for days following. However, some hurricanes will make landfall. Striking an island, especially a mountainous one, could cause its circulation to break down. If it hits a continent, a hurricane will be cut off from its supply of warm, moist maritime air. It will also begin to draw in dry continental air, which combined with increased friction over land leads to the weakening and eventual death of the hurricane. Over mountainous terrain this will be a quick end. But over flat areas, it may take two to three days to break down the circulation. Even then you are still left with a large pocket of tropical moisture which can cause substantial inland flooding. There have been studies on the rate of storm decay once they make landfall (Demaria Kaplan Decay Model). References: Willoughby, H.E. (1990a): “Temporal changes of the primary circulation in tropical cyclones” J. Atmos. Sci., 47, pp.242-264 Willoughby, H.E., J.A. Clos, and M.G. Shoreibah (1982): “Concentric eye walls, secondary wind maxima, and the evolution of the hurricane vortex” J. Atmos. Sci., 39, pp.395-411 Powell, M.D., and S.H. Houston, 1996: “Hurricane Andrew’s wind field at landfall in South Florida. Part II: Applications to real -time analysis and preliminary damage assessment” Wea. Forecasting, 11, pp.329-349 Tuleya, R.E. (1994): “Tropical storm development and decay: Sensitivity to surface boundary conditions” Mon. Wea. Rev., 122, pp.291-304 Tuleya, R.E. and Y. Kurihara (1978): “A numerical simulation of the landfall of tropical cyclones” J. Atmos. Sci., 35, pp.242-257 What Determines the Movement of Tropical Cyclones?Tropical cyclones – to a first approximation – can be thought of as being steered by the surrounding environmental flow throughout the depth of the troposphere (from the surface to about 12 km or 8 mi). Dr. Neil Frank, former director of the U.S. National Hurricane Center, used the analogy that the movement of hurricanes is like a leaf being steered by the currents in the stream, except that for with a hurricane the stream has no set boundaries. Subtropical ridge and its relationship with Cape Verde hurricane tracksIn the tropical latitudes (typically equatorward of 20°-25°N or S), tropical cyclones usually move toward the west with a slight poleward component. This is because there exists an axis of high pressure called the subtropical ridge that extends east-west poleward of the storm. On the equatorward side of the subtropical ridge, general easterly winds prevail. However, if the subtropical ridge is weak – often times due to a trough in the jet stream – the tropical cyclone may turn poleward and then recurve back toward the east. On the poleward side of the subtropical ridge, westerly winds prevail thus steering the tropical cyclone back to the east. These westerly winds are the same ones that typically bring extratropical cyclones with their cold and warm fronts from west to east. Divergent hurricane track due to troughMany times it is difficult to tell whether a trough will allow the tropical cyclone to recurve back out to sea (for those folks on the eastern edges of continents) or whether the tropical cyclone will continue straight ahead and make landfall. For more non-technical information on the movement of tropical cyclones, see Pielke and Pielke’s “Hurricanes: Their Nature and Impacts on Society”. For a more detailed, technical summary on the controls on tropical cyclone motion, see Elsberry’s chapter in “Global Perspectives on Tropical Cyclones”. Storm Surge v. Storm TideStorm surge is an abnormal rise of water generated by a storm’s winds blowing onshore. Storm tide is the combination of the storm surge and astronomical tide as a result of a storm. Storm surge is caused by the force of high wind speeds acting on the ocean surface combined with the forward speed of the storm. The height of a storms surge is determined by the approaching angle of the storm as well as the coastline characteristics, such as the shape of the continental shelf and local geographic features, such as inlets. The degree of vulnerability of any stretch of coast is dependent on a number of factors which includes the central pressure, intensity, forward speed, storm size, angle of approach, width and slope of the off-shore continental shelf, and local bays and inlets. The figure above illustrates the degree of storm surge threat for a “worst case scenario” Category 4 hurricane normalized along the coastline of the eastern and Gulf coasts of the United States. The SLOSH ModelThe Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model is the computer model utilized by the National Oceanic and Atmospheric Administration (NOAA) for coastal inundation risk assessment and the operational prediction of storm surge. The eastern seaboard and Gulf Coast of the United States, Puerto Rico, the Bahamas, the Virgin Islands, and Hawaii, are subdivided into 39 regions or “basins.” These areas represent sections of the coastline that are centered upon particularly susceptible features: inlets, large coastal centers of population, low-lying topography, and ports. The SLOSH model computes the maximum potential impact of the storm in these “computational domains” based on storm intensity, track, and estimates of storm size provided by hurricane specialists at the National Hurricane Center (NHC). Currently, SLOSH basins are being updated at an average rate of 6 basins per year. SLOSH basin updates are ultimately governed by the Interagency Coordinating Committee on Hurricanes (ICCOH). ICCOH manages hazard and post-storm analysis for the Hurricane Evacuation Studies under FEMA’s Hurricane Program. Updates are driven by a number of different factors such as: changes to a basin’s topography/bathymetry due to a hurricane event, degree of vulnerability to storm surge, availability of new data, changes to the coast, and the addition of engineered flood protection devices (e.g. levees). Sometimes these updates include higher grid size resolution to improve surge representation, increasing areas covered by hypothetical tracks for improved accuracy, conversion to updated vertical reference datums, and including the latest topography or bathymetric data for better representation of barrier, gaps, passes, and other local features. The SLOSH model can generate several different products: Deterministic runs Probabilistic (P-surge) runs
P-Surge is available whenever a hurricane watch or warning is in effect. It is posted on the NHC webpage within approximately 30 minutes after the advisory release time. Maximum Envelope of Water (MEOW) runs
Internally a number of parallel SLOSH runs with same intensity, forward speed, storm trajectory, and initial tide level are performed for the basin. The only difference in runs is that each is conducted at some distance to the left or to the right of the main track (typically at the center of the grid). Each component run computes a storm surge value for each grid cell. For example, five parallel runs may yield storm surge values of 4.1, 7.1, 5.3, 6.3, and 3.8 feet. In this case, the MEOW for the cell is 7.1 ft. It is unknown (to the user) which track generated the MEOW for a particular cell, so it is entirely possible that the MEOW values for adjacent cells may have come from different runs. MEOWs are used to incorporate the uncertainties associated with a given forecast and help eliminate the possibility that a critical storm track will be missed in which extreme storm surge values are generated. MEOWs provide a worst case scenario for a particular category, forward speed, storm trajectory, and initial tide level incorporating uncertainty in forecast landfall location. The results are typically generated from several thousand SLOSH runs for each basin. Over 80 MEOWs have been generated for some basins. This product provides useful information aiding in hurricane evacuation planning. Maximum
of MEOW (MOM) runs Strengths and limitations of SLOSH The SLOSH model is computationally efficient resulting in fast computer runs. It is able to resolve flow through barriers, gaps, and passes and model deep passes between bodies of water. It also resolves inland inundation and the overtopping of barrier systems, levees, and roads. It can even resolve coastal reflections of surges such as coastally trapped Kelvin waves. However it does not model the impacts of waves on top of the surge, account for normal river flow or rain flooding, nor does it explicitly model the astronomical tide (although operational runs can be run with different water level anomalies to model conditions at the onset of operational runs). How Much Lightning Occurs in Tropical Cyclones?Surprisingly, not much lightning occurs in the inner core (within about 100 km or 60 mi) of the tropical cyclone center. Only around a dozen or less cloud-to-ground strikes per hour occur around the eyewall of the storm, in strong contrast to an overland mid-latitude mesoscale convective complex which may be observed to have lightning flash rates of greater than 1000 per hour maintained for several hours. Hurricane Andrew’s eyewall had less than 10 strikes per hour from the time it was over the Bahamas until after it made landfall along Louisiana, with several hours with no cloud-to-ground lightning at all (Molinari et al. 1994). However, lightning can be more common in the outer cores of the storms (beyond around 100 km or 60 mi) with flash rates on the order of 100s per hour. This lack of inner core lightning is due to the relative weak nature of the eyewall thunderstorms. Because of the lack of surface heating over the ocean ocean and the “warm core” nature of the tropical cyclones, there is less buoyancy available to support the updrafts. Weaker updrafts lack the super-cooled water (e.g. water with a temperature less than 0° C or 32° F) that is crucial in charging up a thunderstorm by the interaction of ice crystals in the presence of liquid water (Black and Hallett 1986). The more common outer core lightning occurs in conjunction with the presence of convectively-active rainbands (Samsury and Orville 1994). One of the exciting possibilities that recent lightning studies have suggested is that changes in the inner core strikes – though the number of strikes is usually quite low – may provide a useful forecast tool for intensification of tropical cyclones. Black (1975) suggested that bursts of inner core convection which are accompanied by increases in electrical activity may indicate that the tropical cyclone will soon commence a deepening in intensity. Analyses of Hurricanes Diana (1984), Florence (1988) and Andrew (1992), as well as an unnamed tropical storm in 1987 indicate that this is often true (Lyons and Keen 1994 and Molinari et al. 1994). References: Molinari, J., P.K. Moore, V.P. Idone, R.W. Henderson, and A.B. Saljoughy (1994): “Cloud-to-ground lightning in Hurricane Andrew” J. Geophys. Res., pp.16665-16676 Black, R.A., and J. Hallett (1986): “Observations of the distribution of ice in hurricanes” J. Atmos. Sci., 43, pp.802-822 Samsury, C.E., and R.E. Orville, 1994: “Cloud-to-ground lightning in tropical cyclones: A study of Hurricanes Hugo (1989) and Jerry (1989)” Mon. Wea. Rev., 122, pp.1887-1896 Black, P.G., (1975): “Some aspects of tropical storm structure revealed by handheld-camera photographs from space” Skylab Explores the Earth, NASA, pp.417-461 Lyons, W.A., and C. S. Keen (1994): “Observations of lightning in convective supercells within tropical storms and hurricanes” Mon. Wea. Rev., 122, pp.1897-1916 How Does the Ocean Respond to a Hurricane?The ocean’s primary direct response to a hurricane is a cooling of the sea surface temperature (SST). How does this occur? When the strong winds of a hurricane move over the ocean they churn-up much cooler water from below. The net result is that the SST of the ocean after storm passage can be lowered by several degrees Celsius (up to 10° Fahrenheit). A warmer ocean can have intensifying effects because the warmer an ocean is, the easier it is for the liquid water to become vapor and fuel the storm’s clouds. Figure 1 to the left shows SSTs ranging between 25-27°C (77-81°F) several days after the passage of Hurricane Georges in 1998. As Figure 1 illustrates, Georges’ post-storm ‘cold wake’ along and to the right of the superimposed track is 3-5°C (6-9°F) cooler than the undisturbed SST to the west and south (i.e. red/orange regions are ~30°’C [86°’F]). The magnitude and distribution of the cooling pattern shown in this illustration is fairly typical for a post-storm SST analysis. One important caveat to realize however is that most of the 3-5°C (6-9°F) ocean cooling shown in Figure 1 occurs well after the storm has moved away from the region (in this case several days after Georges made landfall). The amount of ocean cooling that occurs directly beneath the hurricane within the high wind region of the storm is a much more important question scientists would like to have answered. Why? Hurricanes get their energy from the warm ocean water beneath them. However, in order to get a more accurate estimate of just how much energy is being transferred from the sea to the storm, scientists need to know ocean temperature conditions directly beneath the hurricane. Unfortunately, with 150kph+ (100mph+) winds, 20m+ (60ft+) seas and heavy cloud cover being the norm in this region of the storm, direct (or even indirect) measurement of SST conditions within the storm’s “inner core” environment are very rare. Thankfully in this case “very rare” does not mean “once in a lifetime”. Recently, scientists in AOML’s Hurricane Research Division (HRD) were able to get a better idea of how much SST cooling occurs directly under a hurricane by looking at many storms over a 28 year period. By combining these rare events, HRD scientists put together a “composite average” of ocean cooling directly under the storm. Figure 2 illustrates that, on average, cooling patterns are a lot less than the post storm 3-5°C (6-9°F) cold wake estimates shown in Figure 1. In most cases, the ocean temperature under a hurricane will range somewhere between 0.2 and 1.2°C (0.4 and 2.2°F) cooler that the surrounding ocean environment. Exactly how much depends on many factors including ocean structure beneath the storm (i.e. location), storm speed, time of year and to a lesser extent, storm intensity (Cione and Uhlhorn 2003).While the estimates in Figure 2 represent a dramatic improvement when it comes to more accurately representing actual SST cooling patterns experienced under a hurricane, even small errors in inner core SST can result in significant miscalculations when it comes to accurately assessing how much energy is transferred from the warm ocean environment directly to the hurricane. With all other factors being equal, being “off” by a mere 0.5°C (1°F) can be the difference between a storm that rapidly intensifies and one that falls apart! With that much at stake, scientists at HRD and other government and academic institutions are working to improve our ability to accurately estimate, observe and predict “under-the-storm” upper ocean conditions. These efforts include statistical studies, modeling efforts and enhanced observational capabilities designed to help scientists better assess upper ocean thermal conditions under the storm. It is believed that future forecasts of tropical cyclone intensity change will be significantly improved. Reference: What Are the Components of a Hurricane such as the Eye, Eyewall, Spiral Bands, and Moat?The Eye is a roughly circular area of fair weather found at the center of a severe tropical storm. The eye is the region of the lowest pressure at the surface and the warmest temperatures at the top. Eye size ranges from 5-120 miles across, but most are 20-40 miles in diameter. Understanding exactly how the eye forms has been controversial. Some scientists believe the radial spreading of the wind creates a warm dry down flow from the upper atmosphere, and this forms the cloud-free eye. Others have think the latent heat release in the eyewall forces the subsidence in the storm center creating the eye. The Eyewall is a ring of deep convection bordering the eye of the storm. This area has the highest surface winds in the tropical cyclone. Because air in the eye is slowly sinking, it creates an updraft in the eyewall. In particularly strong storms, concentric eyewall circles (or an “eyewall replacement cycle”) can occur. Eyewall replacement happens when a storm reaches its intensity threshold and the eye contracts to a smaller size (5-15 miles). Strong rain bands in the outer storm move inward towards the eye, robbing the inner eyewall of its moisture and momentum and weakening the storm. Spiral Bands are long, narrow bands of rain and thunderstorms that are oriented in the same direction as the wind movement. They are caused by convection (the vertical movement of air masses) and they spiral into the center of the tropical cyclone. In contrast, the Moat of a storm usually refers to the region between the eyewall and an outer spiral band where rainfall is relatively lighter. Not all hurricanes have moats. References: Hawkins, H.F., and D.T. Rubsam (1968): “Hurricane Hilda, 1964 : II Structure and budgets of the hurricane on October 1, 1964” Mon. Wea. Rev., 104, pp.418-442 Weatherford, C. and W.M. Gray (1988): “Typhoon structure as revealed by aircraft reconnaissance. Part II: Structural variability” Mon. Wea. Rev., 116, pp.1044-1056 Smith, R.K. (1980): “Tropical Cyclone Eye Dynamics.” J. Atmos. Sci., 37 (6), pp.1227-1232. Willoughby, H.E. (1979): “Forced secondary circulations in hurricanes” J. Geophys. Res., 84, pp.3173-3183 Shapiro, L.J. and H.E. Willoughby (1982): “The Response of Balanced Hurricanes to Local Sources of Heat and Momentum” J. Atmos. Sci., 39 (2), pp.378-394 Willoughby, H.E. (1990a): “Temporal changes of the primary circulation in tropical cyclones” J. Atmos. Sci., 47, pp.242-264 Willoughby, H.E. (1995): “Mature structure and evolution. Global Perspectives on Tropical Cyclones, R.L. Elsberry (ed.). World Meteorological Organization, Report No. TCP-38; Geneva, Switzerland, 62 pp. What is the 'dirty side' of a storm? Why Are a Hurricane's Winds Higher on its Right Side?Tropical cyclones tend to be symmetrical. This means the winds should be the same in all quadrants at a given distance from the center. However, most hurricanes are moving, and the storm’s motion will be added to or subtracted from those winds creating an asymmetric structure. The side where the motion is added to the winds is called the “dirty side” as the weather is rougher and more dangerous there. The “right side” is in reference to the storm’s direction of movement in the Northern Hemisphere. If a hurricane is moving to the west, the right side would be to the north of the storm, if it is heading north, then the right side would be to the east of the storm. In the Southern Hemisphere, this is reversed since a tropical cyclone’s winds spiral around its center clockwise there as opposed to counterclockwise in the Northern Hemisphere. So south of the Equator the “dirty side” is the “left side” of the cyclone. Northern Hemisphere Southern HemisphereFor example, a hurricane with 90mph winds moving at 10mph would have a 100mph wind speed on the forward-moving side and 80 mph on the side with the backward motion. Weather forecast advisories already take this asymmetry into account and, in this case, would state that the highest winds were 100 mph [160 km/hr]. How Much Energy does a Hurricane Produce?The energy released from a hurricane can be explained in two ways: the total amount of energy released by the condensation of water droplets (latent heat), or the amount of kinetic energy generated to maintain the strong, swirling winds of a hurricane. The vast majority of the latent heat released is used to drive the convection of a storm, but the total energy released from condensation is 200 times the world-wide electrical generating capacity, or 6.0 x 1014 watts per day. If you measure the total kinetic energy instead, it comes out to about 1.5 x 1012 watts per day, or ½ of the world-wide electrical generating capacity. It would seem that although wind energy seems to be the most obvious energetic process, it is actually the latent release of heat that feeds a hurricane’s momentum. To Calculate:
Reference: Emanuel, K. A., (1999): “The power of a hurricane: An example of reckless driving on the information superhighway” Weather, 54, 107-108 Are There Hurricanes on Other Planets?There are no other planets known to have warm water oceans from which true water cloud hurricanes can form. However, many astronomers and planetary meteorologists believe gas giant planets such as Jupiter and Saturn exhibit similar storms. The principal candidate is the famous Great Red Spot (GRS) on Jupiter, and the numerous whorls that surround it, where ammonia takes the place of water. The GRS exhibits an anticyclonic circulation at its top, just as tropical cyclones do at the top of the troposphere. On Saturn, a polar storm has been spotted by the Cassini spacecraft measuring up to 1,250 miles in diameter, about 20 time larger than an Earthly hurricane with winds four times stronger. On Mars, a large, cyclonic cloud feature forms every year in the northern hemisphere. It forms in the morning and dissipates by the afternoon. This cloud is likely composed of water/ice and is white in appearance. It doesn’t appear to rotate but is about 1000 miles wide with an inner hole or ‘eye’ about 200 miles across. Over 3,400 extrasolar planets have been found to date, but no others are confirmed to have convectively driven storms. However, there is reason to believe such storms exist on extrasolar planets as well. Hurricane Forecasting and PreparednessWhen Is Hurricane Season?The Atlantic hurricane season is June 1st to November 30th. In the East Pacific, it runs from May 15th to November 30th. Hurricane Awareness week runs from May 25th through May 31st and is a great time to get your hurricane kit and plans up to date. NOAA’s seasonal outlook is published here: NOAA Seasonal Outlook Hurricanes have occurred outside of the official six month season , but these dates were selected to encompass the majority of Atlantic tropical cyclone activity (over 97%). When the Weather Bureau organized its new hurricane warning network in 1935 it scheduled a special telegraph line to connect the various centers to run from June 15th through November 15th. Those remained the start and end dates of the ‘official’ season until 1964, when it was decided to end the season on November 30th, and in 1965, when the start was moved to the beginning of June. These changes made the Atlantic hurricane season six months long and easier for people to remember. The Atlantic basin (figure 1) shows a very peaked season from August through October, with 78% of the tropical storm days, 87% of the minor hurricane days, and 96% of the major hurricane days occurring then (Landsea (NHC) 1993). Maximum activity occurs in early to mid September. “Out of season” tropical cyclones primarily occur in May or December.The Northeast Pacific basin has a broader peak with activity beginning in late May or early June and going until late October or early November with a peak in storminess in late August/early September. The National Hurricane Center’s official dates for this basin are from May 15th to November 30th.The Northwest Pacific basin has tropical cyclones occurring all year round regularly. There is no official definition of typhoon season for this reason. There is a distinct minimum in February and the first half of March, and the main season goes from July to November with a peak in late August/early September.The North Indian basin has a double peak of activity in May and November though tropical cyclones are seen from April to December. The severe cyclonic storms (>33 m/s winds [76 mph]) occur almost exclusively from April to June and late September to early December. The Southwest Indian and Australian/Southeast Indian basins have very similar annual cycles with tropical cyclones beginning in late October/early November, reaching a double peak in activity – one in mid-January and one in mid-February to early March, and then ending in May. The Australian/Southeast Indian basin February lull in activity is a bit more pronounced than the Southwest Indian basin’s lull. The Australian/Southwest Pacific basin begin with tropical cyclone activity in late October/early November, reaches a single peak in late February/early March, and then fades out in early May. Globally, September is the most active month and May is the least active month. (Neumann 1993) References: Neumann, C.J., B.R. Jarvinen, C.J. McAdie, and J.D. Elms (1993): Tropical Cyclones of the North Atlantic Ocean, 1871-1992, Prepared by the National Climatic Data Center, Asheville, NC, in cooperation with the NHC, Coral Gables, FL, 193pp. How Can I Prepare for a Hurricane?The best time to prepare is before hurricane season begins. Make a plan for you and your family about what to do if a hurricane threatens. Put together a hurricane kit. Ensure your house is up to code, and check for problems, such as overhanging branches or missing roof tiles. Check your shutters and other window and door coverings. Once the season begins, stay informed. Check the outlook every day, and if anything is threatening keep updated on the latest advisories. For hurricane preparation tips, check out FEMA’s comprehensive downloadable guidebook and visit www.ready.gov/hurricanes for the best information available on hurricane preparedness. Don’t forget to sign up for wireless emergency alerts. Alternatively, you can get updates from NOAA Radio or Radio Fax (for mariners). What Factors Produce the Most Damage?The mean annual damage from hurricanes in the US is 9.5 billion dollars, when we adjust not only for inflation but for the increase in value of real goods in average households. Hurricane damage varies greatly from year to year, depending on the number and strength of hurricanes making landfall, but there does not seem to be a long-term trend in adjusted damage over the last century. There is very little association between the physical size of a hurricane and its intensity. A big hurricane does not have to be an intense one and vice versa. The damage a hurricane can cause is a function of both its maximum sustained wind and the extent of the hurricane force winds. A broad, weak storm may cause as much damage as a small, strong one. It is false to think that damage is linear with wind speed, that a 150-mph winds will cause twice the damage as a 75-mph winds. The relationship is exponential, and not linear. A category 5 storm could cause up to 250 times the damage of a category 1 hurricane of the same size.
References: Weatherford, C. and W.M. Gray (1988): “Typhoon structure as revealed by aircraft reconnaissance. Part II: Structural variability” Mon. Wea. Rev., 116, pp.1044-1056 Pielke, Jr. R. A., and C. W. Landsea, 1998: “Normalized Atlantic hurricane damage 1925-1995” Wea. Forecasting, 13, pp.621-631 What is it like to go Through a Hurricane on the Ground? What are the Early Warning Signs of an Approaching Tropical CycloneJust as every person is an individual, every hurricane is different. So every experience with such a storm will be unique. The summary below is of a general sequence of events one might expect from a Category 2 hurricane approaching a coastal area. What you might experience could be vastly different.
Last updated August 13, 2004 How Do They Estimate Hurricane Strength From Satellite?Hurricane forecasters estimate tropical cyclone strength from satellite using a method called the Dvorak technique. Vern Dvorak developed the scheme in the early 1970s using a pattern recognition decision tree (Dvorak 1975, 1984). Utilizing the current satellite picture of a tropical cyclone, one matches the image versus a number of possible pattern types: Curved band Pattern, Shear Pattern, Eye Pattern, Central Dense Overcast (CDO) Pattern, Embedded Center Pattern or Central Cold Cover Pattern. If infrared satellite imagery is available for Eye Patterns (generally the pattern seen for hurricanes, severe tropical cyclones and typhoons), then the scheme utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops. The larger the difference, the more intense the tropical cyclone is estimated to be. From this one gets a “T-number” and a “Current Intensity (CI) Number”. CI numbers have been calibrated against aircraft measurements of tropical cyclones in the Northwest Pacific and Atlantic basins. On average, the CI numbers correspond to the following intensities: Current Intensity Numbers
Note that this estimation of both maximum winds and central pressure assumes that the winds and pressures are always consistent. However, since the winds are really determined by the pressure gradient, small tropical cyclones (like the Atlantic’s Andrew in 1992, for example) can have stronger winds for a given central pressure than a larger tropical cyclone with the same central pressure. Thus caution is urged in not blindly forcing tropical cyclones to “fit” the above pressure- wind relationships. (The reason that lower pressures are given to the Northwest Pacific tropical cyclones in comparison to the higher pressures of the Atlantic basin tropical cyclones is because of the difference in the background climatology. The Northwest Pacific basin has a lower background sea level pressure field. Thus to sustain a given pressure gradient and thus the winds, the central pressure must accordingly be smaller in this basin.) The errors for using the above Dvorak technique in comparison to aircraft measurements taken in the Northwest Pacific average 10 mb with a standard deviation of 9 mb (Martin and Gray 1993). Atlantic tropical cyclone estimates likely have similar errors. Thus an Atlantic hurricane that is given a CI number of 4.5 (winds of 77 kt and pressure of 979 mb) could in reality be anywhere from winds of 60 to 90 kt and pressures of 989 to 969 mb. These would be typical ranges to be expected; errors could be worse. However, in the absence of other observations, the Dvorak technique does at least provide a consistent estimate of what the true intensity is. While the Dvorak technique was calibrated for the Atlantic and Northwest Pacific basin because of the aircraft reconnaissance data ground truth, the technique has also been quite useful in other basins that have limited observational platforms. However, at some point it would be preferable to re-derive the Dvorak technique to calibrate tropical cyclones with available data in the other basins. Lastly, while the Dvorak technique is primarily designed to provide estimates of the current intensity of the storm, a 24 h forecast of the intensity can be obtained also by extrapolating the trend of the CI number. Whether this methodology provides skillful forecasts is unknown. References: Dvorak, V.F., 1975: “Tropical cyclone intensity analysis and forecasting from satellite imagery” Mon. Wea. Rev., 103, pp.420-430 Dvorak, V.F., 1984: “Tropical cyclone intensity analysis using satellite data” NOAA Tech. Rep. NESDIS 11, 47pp Fitzpatrick, P.J., J.A. Knaff, C.W. Landsea, and S.V. Finley (1995): “A systematic bias in the Aviation model’s forecast of the Atlantic tropical upper tropospheric trough: Implications for tropical cyclone forecasting” Wea. Forecasting, 10, pp.433-446 Martin, J.D., and W.M. Gray (1993): “Tropical cyclone observation and forecasting with and without aircraft reconnaissance” Wea. Forecasting, 8, pp.519-532 How Is Storm Surge Observed, Measured, and Forecast?Observations & MeasurementsThere are several methods used by NOAA, the United States Geological Survey (USGS), and the Federal Emergency Management Agency (FEMA) to measure storm surge. Each method has advantages and draw backs. Post-storm analysis of storm surge requires resolving differences in what each measures in order to find the best approximation of the surge heights. Tide Stations (NOAA) Check your coastal marine forecast at NOAA’s Tides & Currents Website.A network of 175 long-term, continuously operating water level stations located throughout the U.S. serving as the foundation for NOAA’s tide prediction products. Measures still water (e.g. no waves) Traditionally the most reliable method Limited, fixed stations High Water Marks (USGS / FEMA) Perishable Traditionally best method for capturing highest surge level Subjective and often includes impact of waves Pressure Sensors (USGS) Relatively new method Mobile, deployed in advance of storms at expected location of highest surge Can contain impact of waves ForecastingThe Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model is the computer model utilized by the National Oceanic and Atmospheric Administration (NOAA) for coastal inundation risk assessment and the operational prediction of storm surge. The eastern seaboard and Gulf Coast of the United States, Puerto Rico, the Bahamas, the Virgin Islands, and Hawaii, are subdivided into 39 regions or “basins.” These areas represent sections of the coastline that are centered upon particularly susceptible features: inlets, large coastal centers of population, low-lying topography, and ports. The SLOSH model computes the maximum potential impact of the storm in these “computational domains” based on storm intensity, track, and estimates of storm size provided by hurricane specialists at the National Hurricane Center. Who Makes the Hurricane Forecasts and How Accurate Are They?NHC and CPHC issue an official forecast, every six hours, of the center position, maximum one-minute surface (10 meter [33 ft] elevation) wind speed (intensity), and radii of the 34 knot (39 mph,63 kph), 50 knot (58 mph,92 kph), and 64 knot (74 mph,117 kph) wind speeds in four quadrants (northeast, southeast, southwest, and northwest) surrounding the cyclone. NHC’s Track and Intensity forecasts have both improved substantially over the years and continue to improve. Today a 3-day forecast is as accurate as those issued for a 2-day prediction in the late 1980s. However, much work still remains to better understand and predict wind intensity changes in tropical storms and hurricanes. These official forecasts are later verified and then consolidated into a “best track” for the storm. The Best Track has a center position and maximum wind speed value for each six-hour time that represents the official NHC estimate of the location and intensity of a tropical cyclone. Values of central pressure and the radii of hurricane-force and gale-force winds may also be included as well as other significant events, such as landfall or peak intensity, especially if they occur other than the six-hourly times. The Best Tracks are included in the Tropical Cyclone Reports issued by NHC and CPHC after hurricane season. They are also included in the official hurricane database HURDAT2. What Is the Difference Between a Hurricane Watch and a Hurricane Warning?
The National Hurricane Center has a great Glossary of Terms that are used in weather forecasts. Some important terms from that glossary are below. Hurricane Watch – A Hurricane Watch is an announcement that hurricane force winds are possible within the specified area in association with a tropical cyclone. A hurricane watch is issued 48 hours in advance of the anticipated onset. Hurricane Warning – Hurricane warnings are issued 36 hours in advance and are announced when hurricane force winds are expected somewhere within the specified area in association with a cyclone. This warning can remain in effect in the face of other hazards, such as flooding even if the winds drop to below hurricane force. Advisory – An advisory contains all tropical cyclone watches and warnings in effect along with details concerning tropical cyclone locations, intensity and movement, and precautions to be taken. Maximum sustained wind – This is determined as winds that last for an average of at least one minute at the surface of a hurricane or about 33 feet (10 meters). Gusts – are classified as a 3-5 second burst of wind higher than the maximum sustained wind. Storm Surge Watch – A storm surge watch is the possibility of a life-threatening inundation from rising water moving inland from the shoreline, and it is usually issued 48 hours from the anticipated event in association with an ongoing tropical storm. Storm Surge Warning – The danger of a life-threatening inundations from rising water moving inland, and usually issued 36 hours in advance of the event in association with an ongoing tropical storm. Storm Track – A storm track is a representation of a tropical cyclone’s predicted path, location, and intensity over its lifetime. The best track contains the cyclone’s latitude, longitude, maximum sustained winds, and minimum sea level pressure at 6-hour intervals. Storm Intensity – Hurricane intensity refers to the amount of energy a hurricane is carrying with it. Hurricane intensity and size are not closely related. Reference: Powell, M.D., S.H. Houston, and T.A. Reinhold, 1996:”Hurricane Andrew’s Landfall in South Florida, Part I: Standardizing measurements for documentation of surface wind fields.” Wea. Forecast. v.11, p.329-349 How Does AOML Contribute to hurricane forecasting?The Atlantic Oceanographic and Meteorological Laboratory (AOML) supports these organizations by doing hurricane research with both observations and model experiments in order to provide guidance and integrate new technology into the forecast models. These experimental models are tested rigorously and submitted to the NCEP for verification before they are integrated into the operational models and sent to the NHC for use in the public forecast. Who Makes the Seasonal Forecast and How Accurate Are They?There are a number of different seasonal forecasts currently being issued for various basins. Some of these are fairly new, while the oldest and most well known (Prof. Bill Gray’s forecast from CSU) has been issued for almost two decades. Click here for a comparison of the CSU and NOAA seasonal numbers. North Atlantic Basin:
NE Pacific Basin:
NW Pacific Basin:
Australian Basin:
South China Sea:
South Pacific Basin:
What Are the Current Hurricane Track and Intensity Models?The major hurricane track forecast models run operationally for the Atlantic, Eastern Pacific, and Central Pacific hurricane basins are:
The full list of models used in the Atlantic and Eastern and Central Pacific is available to download here. Various types of consensus models (ensemble means) are available from these models. Despite the variety of hurricane track forecast models, there are only a few models that provide operational intensity change forecasts for the Atlantic and Eastern and Central Pacific basins:
Information on the performance of these models is available after each season here. References: Aberson, Sim D. (1998): “Five-day tropical cyclone track forecasts in the North Atlantic basin” Weather and Forecasting, 13, pp.1005-1015 Marks, D.G. (1992): “The beta and advection model for hurricane track forecasting” NOAA Tech. Memo. NWS NMC 70, Natl. Meteorological Center; Camp Springs, Maryland, 89 pp. Lord, S.J. (1993): “Recent developments in tropical cyclone track forecasting with the NMC global analysis and forecast system” Preprints of the 20th Conference on Hurricanes and Tropical Meteorology, San Antonio, Amer. Meteor. Soc., pp.290-291 Bender, M.A., R.J. Ross, R.E. Tuleya, and Y. Kurihara (1993): “Improvements in tropical cyclone track and intensity forecasts using the GFDL initialization system” Mon. Wea. Rev., 121, pp.2046-2061 Gopalakrishnan, S.G., S. Goldenberg, T. Quirino, X. Zhang, F. Marks, K-S Yeh, R. Atlas, V. Tallapragada (2012): “Toward Improving High-Resolution Numerical Hurricane Forecasting: Influence of Model Horizontal Grid Resolution, Initialization, and Physics” Wea. Forecasting, 27, pp.647-666. Radford, A.M. (1994): “Forecasting the movement of tropical cyclones at the Met. Office” Met. Apps., 1, pp.355-363 Fiorino, M., J.S. Goerss, J.J. Jensen, E.J. Harrison, Jr.(1993): “An evaluation of the real-time tropical cyclone forecast skill of the Navy operations global atmospheric prediction system in the western North Pacific” Wea. Forecasting, 8, pp.3-24 Jarvinen, B.R., and C.J. Neumann (1979): “Statistical forecast of tropical cyclone intensity” NOAA Tech. Memo. NS NHC-10, 22pp. DeMaria, M. and J. Kaplan (1994): “A statistical hurricane intensity prediction scheme (SHIPS) for the Atlantic basin” Wea. Forecasting, 9, pp.209-220 Attempts to Stop a Hurricane in its TrackWhat was Project Stormfury?The U.S. Government once supported research into methods of hurricane modification, known as Project STORMFURY. It was an ambitious experimental program of research on hurricane modification carried out between 1962 and 1983. The proposed modification technique involved artificial stimulation of convection outside the eyewall through seeding with silver iodide. The invigorated convection, it was argued, would compete with the original eyewall, lead to the reformation of the eyewall at larger radius, and thus, through partial conservation of angular momentum, produce a decrease in the strongest winds. Since a hurricane’s destructive potential increases rapidly as its strongest winds become stronger, a reduction as small as 10% would have been worthwhile. Modification was attempted in four hurricanes on eight different days. On four of these days, the winds decreased by between 10 and 30%, The lack of response on the other days was interpreted to be the result of faulty execution of the seeding or of poorly selected subjects. These promising results came into question in the mid-1980s because observations in unmodified hurricanes indicated:
For a couple decades NOAA and its predecessor tried to weaken hurricanes by dropping silver iodide – a substance that serves as an effective ice nuclei – into the rainbands of the storms. During the STORMFURY years, scientists seeded clouds in Hurricanes Esther (1961), Beulah (1963), Debbie (1969), and Ginger (1971). The experiments took place over the open Atlantic far from land. The STORMFURY seeding targeted convective clouds just outside the hurricane’s eyewall in an attempt to form a new ring of clouds that, hopefully, would compete with the natural circulation of the storm and weaken it. The idea was that the silver iodide would enhance the thunderstorms of a rainband by causing the supercooled water to freeze, thus liberating the latent heat of fusion and helping a rainband to grow at the expense of the eyewall. With a weakened convergence to the eyewall, the strong inner core winds would also weaken quite a bit. For cloud seeding to be successful, the clouds must contain sufficient supercooled water (water that has remained liquid at temperatures below the freezing point, 0°C/32°F). Neat idea, but in the end it had a fatal flaw. Observations made in the 1980s showed that most hurricanes don’t have enough supercooled water for STORMFURY seeding to work – the buoyancy in hurricane convection is fairly small and the updrafts correspondingly small compared to the type one would observe in mid-latitude continental super or multicells. In addition, it was found that unseeded hurricanes form natural outer eyewalls just as the STORMFURY scientists expected seeded ones to do. This phenomenon makes it almost impossible to separate the effect (if any) of seeding from natural changes. The few times that they did seed and saw a reduction in intensity was undoubtedly due to what is now called “concentric eyewall cycles.” Thus nature accomplishes what NOAA had hoped to do artificially. No wonder the first few experiments were thought to be successes. Because the results of seeding experiments were so inconclusive, STORMFURY was discontinued. A special committee of the National Academy of Sciences concluded that a more complete understanding of the physical processes taking place in hurricanes was needed before any additional modification experiments. The primary focus of NOAA’s Hurricane Research Division today is better physical understanding of hurricanes and improvement of forecasts. To learn about the STORMFURY project as it was called, read Willoughby et al. (1985). Reference: Willoughby, H.E., D.P. Jorgensen, R.A. Black, and S.L. Rosenthal (1985): “Project STORMFURY: A scientific chronicle 1962-1983” Bull. Amer. Meteor. Soc., 66, cover and pp.505-514 What Else has been Considered to Stop a Hurricane?There have been numerous techniques that have been considered over the years to modify hurricanes: seeding clouds with dry ice or silver iodide, reducing evaporation from the ocean surface with thin-layers of polymers, cooling the ocean with cryogenic material or icebergs, changing the radiational balance in the hurricane environment by absorption of sunlight with carbon black, flying jets clockwise in the eyewall to reverse the flow, exploding the hurricane apart with hydrogen bombs, and blowing the storm away from land with giant fans, etc. As carefully reasoned as some of these suggestions are, they all share the same shortcoming: They fail to appreciate the size and power of tropical cyclones. For example, when Hurricane Andrew struck South Florida in 1992, the eye and eyewall devastated a swath 20 miles wide. The heat energy released around the eye was 5,000 times the combined heat and electrical power generation of the Turkey Point nuclear power plant over which the eye passed. The kinetic energy of the wind at any instant was equivalent to that released by a nuclear warhead. Human beings are used to dealing with chemically complex biological systems or artificial mechanical systems that embody a small amount (by geophysical standards) of high-grade energy. Because hurricanes are chemically simple –air and water vapor – introduction of catalysts is unpromising. The energy involved in atmospheric dynamics is primarily low-grade heat energy, but the amount of it is immense in terms of human experience. Attacking weak tropical waves or depressions before they have a chance to grow into hurricanes isn’t promising either. About 80 of these disturbances form every year in the Atlantic basin, but only about 5 become hurricanes in a typical year. There is no way to tell in advance which ones will develop. If the energy released in a tropical disturbance were only 10% of that released in a hurricane, it is still a lot of power. The hurricane police would need to dim the whole world’s lights many times a year. Maybe the time will come when men and women can travel at nearly the speed of light to the stars, and we will then have enough energy for brute-force intervention in hurricane dynamics. Until then, perhaps the best solution is not to try to alter or destroy the tropical cyclones, but just learn to co-exist with them. Since we know that coastal regions are vulnerable to the storms, building codes that can have houses stand up to the force of the tropical cyclones need to be enforced. The people that choose to live in these locations should be willing to shoulder a fair portion of the costs in terms of property insurance – not exorbitant rates, but ones which truly reflect the risk of living in a vulnerable region. In addition, efforts to educate the public on effective preparedness needs to continue. Helping other nations in their mitigation efforts can also result in saving countless lives. Finally, we need to continue in our efforts to better understand and observe hurricanes in order to more accurately predict their development, intensification, and track. References: Simpson, R.H. and J. Simpson (1966): “Why experiment on tropical hurricanes ?” Trans. New York Acad. Sci., 28, pp.1045-1062 Gray, W.M., W.M. Frank, M.L. Corrin, C.A. Stokes (1976): “Weather modification by carbon dust absorption of solar energy” J. Appl. Meteor., 15, pp.355-386 Gray, W.M., W.M. Frank, M.L. Corrin, C.A. Stokes, 1976: Weather Modification by Carbon Dust Absorption of Solar Energy, J. of Appl. Meteor., 15 4, pp. 355-386. Woodcock, A.H., D.C. Blanchard, C.G.H. Rooth, 1963: Salt-Induced Convection and Clouds, J. of Atmos. Sci., 20, 2, pp. 159-169. Blanchard, D.C., A.H. Woodcock, 1980: The Production, Concentration, and Vertical Distribution of the Sea-salt Aerosol, Ann. NY Acad. Sci., 338, 1, p. 330-347. During each hurricane season, someone always asks “why don’t we destroy tropical cyclones by nuking them” or “can we use nuclear weapons to destroy a hurricane?” There always appear suggestions that one should simply nuke hurricanes to destroy the storms. Apart from the fact that this might not even alter the storm, this approach neglects the problem that the released radioactive fallout would fairly quickly move with the tradewinds to affect land areas and cause devastating environmental problems. Needless to say, this is not a good idea. Now for a more rigorous scientific explanation of why this would not be an effective hurricane modification technique. The main difficulty with using explosives to modify hurricanes is the amount of energy required. A fully developed hurricane can release heat energy at a rate of 5 to 20×1013 watts and converts less than 10% of the heat into the mechanical energy of the wind. The heat release is equivalent to a 10-megaton nuclear bomb exploding every 20 minutes. According to the 1993 World Almanac, the entire human race used energy at a rate of 1013 watts in 1990, a rate less than 20% of the power of a hurricane. If we think about mechanical energy, the energy at humanity’s disposal is closer to the storm’s, but the task of focusing even half of the energy on a spot in the middle of a remote ocean would still be formidable. Brute force interference with hurricanes doesn’t seem promising. In addition, an explosive, even a nuclear explosive, produces a shock wave, or pulse of high pressure, that propagates away from the site of the explosion somewhat faster than the speed of sound. Such an event doesn’t raise the barometric pressure after the shock has passed because barometric pressure in the atmosphere reflects the weight of the air above the ground. For normal atmospheric pressure, there are about ten metric tons (1000 kilograms per ton) of air bearing down on each square meter of surface. In the strongest hurricanes there are nine. To change a Category 5 hurricane into a Category 2 hurricane you would have to add about a half ton of air for each square meter inside the eye, or a total of a bit more than half a billion (500,000,000) tons for a 20 km radius eye. It’s difficult to envision a practical way of moving that much air around. Attacking weak tropical waves or depressions before they have a chance to grow into hurricanes isn’t promising either. About 80 of these disturbances form every year in the Atlantic basin, but only about 5 become hurricanes in a typical year. There is no way to tell in advance which ones will develop. If the energy released in a tropical disturbance were only 10% of that released in a hurricane, it’s still a lot of power, so that the hurricane police would need to dim the whole world’s lights many times a year. Adding Hygroscopic Particles Hygroscopic refers to a substance that binds preferentially with water vapor molecules. Anyone who has used a salt shaker on a humid summer day understands- the salt clumps. The barrier to this method is the assumptions and uncertainties in such a project that would require extensive testing first. More on the SubjectSome people have proposed seeding the inflow layer of a hurricane with granules of some hygroscopic substance. The hope is that these granules will help form tiny cloud droplets, many more than would form naturally. This would tend to ‘lock up’ the moisture in small droplets, rather than allowing the formation of large drops, which tend to fall out as rainfall. This would cause a weight burden on the inflow, and reduce the hurricane’s winds. There are several assumptions made in this chain of logic. The first is that there are too few cloud condensation nuclei (CCN) available naturally. If there aren’t, then adding more wouldn’t change things. The next assumption is that more numerous but smaller cloud drops wouldn’t coalesce into larger drops, even in the turbulent updraft of a hurricane eyewall. And lastly, it assumes that the increased burden on the updraft outweighs the increase in latent heat released when more liquid water reaches the freezing level. If less water is precipitating out, then more will be freezing. That’s a lot of assumptions, and it would have to be proven in computer models first, then in field tests, that they are valid. Otherwise, you would expend a great deal of money and effort, but not change a hurricane sufficiently. “Dyn-O-Gel” is a special powder (produced by Dyn-O-Mat) that absorbs large amounts of moisture and then becomes a gooey gel. It has been proposed to drop large amounts of the substance into the clouds of a hurricane to dissipate some of the clouds thus helping to weaken or destroy the hurricane. At HRD we tried the one possible way that “Dyn-O-Gel” could weaken a hurricane in the MM5 numerical model. We saw an effect but it was small (~1 m/s). The argument was that the glop would make raindrops lumpy (i. e., non-aerodynamic) they would fall slower and increase condensate loading, thus weakening the eyewall updraft. If, by contrast, one increases the fall speed of the hydrometeors, the storm strengthens (again by only ~1 m/s). In the numerical experiments “decrease” meant reduce the fall velocity to half the real value, and “increase” meant double the real value. The foregoing effect is larger than anything one could hope to produce in the real atmosphere. The observation that the experiment that “Dyn-O-Gel” conducted actually “dissipated” clouds is problematic. Did they watch any unmodified clouds ? Isolated Florida cumuli have short lifetimes, and these are just the ones an experimenter would logically pick. Accepting for the sake of argument that they actually did have an effect, the descriptions seem more consistent with an increase in hydrometeor fall speed and accelerated collision coalescence, which the numerical model results argue would strengthen the hurricane, but not much. If this speculation proves to be correct, “Dyn-O-Gel” might be useful for rainmaking during a dry spell, unlike glaciogenic seeding which (in the tropics at least) tends to make rainy days even more rainy–if it does anything at all. One of the biggest problems is, however, that it would take a lot of the stuff to even hope to have an impact. 2 cm of rain falling over 1 square kilometer of surface deposits 20,000 metric tons of water. At the 2000-to-one ratio that the “Dyn-O-Gel” folks advertise, each square km would require 10 tons of goop. If we take the eye to be 20 km in diameter surrounded by a 20km thick eyewall, that’s 3,769.91 square kilometers, requiring 37,699.1 tons of “Dyn-O-Gel”. A C-5A heavy-lift transport airplane can carry a 100 ton payload. So that treating the eyewall would require 377 sorties. A typical average reflectivity in the eyewall is about 40 dB(Z), which works out to 1.3 cm/hr rain rate. Thus to keep the eyewall doped up, you’d need to deliver this much “Dyn-O-Gel” every hour-and-a-half or so. If you crank the reflectivity up to 43 dB(Z) you need to do it every hour. (If the eyewall is only 10 km thick, you can get by with 157 sorties every hour-and-a-half at the lower reflectivity.) Altering the Heat Balance It was hypothesized to absorb sunlight and transfer heat such as black carbon, but it has not been carried out in real life. Additionally, it would likely have negative environmental and ecological consequences, and if added in the wrong place, it could even intensify the storm. More on the SubjectThe idea here is to spread a layer of sunlight absorbing or reflecting particles (such as micro-encapsulated soot, carbon black, or tiny reflectors) at high altitude around a hurricane. This would prevent solar radiation from reaching the surface and cooling it, while at the same time increase the temperature of the upper atmosphere. Being vertically oriented, tropical cyclones are driven by energy differences between the lower and upper layer of the troposphere. Reducing this difference should reduce the forces behind hurricane winds. It would take a tremendous amount of whichever substance you choose to alter the energy balance over a wide swath of the ocean in order to have an impact on a hurricane. One would hope that this substance would eventually disperse or disintegrate and not have a terrible impact on the earth’s ecology. Knowing where to place it would also be tricky. You don’t want to heat up the wrong area of the atmosphere or you could put more energy into the cyclone. These proposals would require a great deal of precisely-timed, coordinated activity to spread the layer, while running the risk of doing more harm than good. Many computer simulations should be run before any field test were tried. Preventing Evaporation with Chemicals There has been some experimental work in trying to develop a liquid that when placed over the ocean surface would prevent evaporation from occurring. If this worked in the tropical cyclone environment, it would probably have a limiting effect on the intensity of the storm as it needs huge amounts of oceanic evaporation to continue to maintain its intensity (Simpson and Simpson 1966). However, finding a substance that would be able to stay together in the rough seas of a tropical cyclone proved to be the downfall of this idea. There was also suggested about 20 years ago (Gray et al. 1976) that the use of carbon black (or soot) might be a good way to modify tropical cyclones. The idea was that one could burn a large quantity of a heavy petroleum to produce vast numbers of carbon black particles that would be released on the edges of the tropical cyclone in the boundary layer. These carbon black aerosols would produce a tremendous heat source simply by absorbing the solar radiation and transferring the heat directly to the atmosphere. This would provide for the initiation of thunderstorm activity outside of the tropical cyclone core and, similarly to STORMFURY, weaken the eyewall convection. This suggestion has never been carried out in real-life. Oil slicks are patchy, and likely would not cover a big enough area to affect the hurricane. It is also difficult to predict and control how and where the oil will move when affected by the storm. If oil happens to spill and there is a storm, the oil could be carried into or away from the coastline depending on its track, but generally the storm will have a dispersing effect. More on the Subject
Will there be oil in the rain related to a hurricane that passed over an oil slick?
How will an oil slick be affected by a hurricane?
The largest impediment to this has to do with the energy expression of the hurricane. Even though a hurricane has huge amounts of energy, it is spread over a massively large area. In essence you would need wind turbine fields dozens of miles wide could both be anchored to receive the energy and mobile to follow the storms. Those systems would also need to withstand windblown debris and transmit the energy. Cooling with Icebergs or Deep Water There have been proposals to tow icebergs to the Atlantic and cool sea surface temperatures, or to pump deep water to the surface. The problem with this is both the size scale and the movement of the hurricane, not to mention the track uncertainty and ecological implications. More on the SubjectSince hurricanes draw their energy from warm ocean water, some proposals have been put forward to tow icebergs from the arctic zones to the tropics to cool the sea surface temperatures. Others have suggested pumping cold bottom water in pipes to the surface, or releasing bags of cold freshwater from near the bottom to do this. Consider the scale of what we are talking about. The critical region in the hurricane for energy transfer would be under or near the eyewall region. If the eyewall was thirty miles (48 kilometer) in diameter, that means an area of nearly 2000 square miles (4550 square kilometers). Now if the hurricane is moving at 10 miles an hour (16 km/hr) it will sweep over 7200 square miles (18,650 square kilometers) of ocean. That’s a lot of icebergs for just 24 hours of the cyclone’s life. Now add in the uncertainty in the track, which is currently 100 miles (160 km) at 24 hours and you have to increase your cool patch by 24,000 sq mi (38,000 sq km). For the iceberg towing method you would have to increase your lead time even more (and hence the uncertainty and area cooled) or risk your fleet of tugboats getting caught by the storm. For the bag/pipe method you would have to preposition your system across all possible approaches for hurricanes. Just for the US mainland from Cape Hatteras to Brownsville would mean covering 528,000 sq mi (850,000 sq km) of ocean floor with devices. Lastly, consider the creatures of the sea. If you suddenly cool the surface layer of the ocean (and even turn it temporarily fresh), you would alter the ecology of that area and probably kill most of the sea life contained therein. A hurricane would be devastating enough on them without our adding to the mayhem. Seeding clouds, towing icebergs, and blowing up hurricanes with nukes all fail to appreciate the size and power of a tropical cyclone. When Andrew hit in 1992, the eye and eyewall devastated a swath 20 miles wide. The heat energy released there was 5,000 times the combined heat and electrical power generation of the Turkey Point nuclear power plant over which the eye had passed. Attacking every tropical disturbance that comes our way is not an efficient use of time either, since only 5 out of 80 become hurricanes in a given year. The best way to minimize the damage of hurricanes is to learn to co-exist with them. Proper building codes and understanding the assumption of risk by choosing to live in a hurricane-prone area can help people evaluate their situation. Smart hurricane prep and public education, along with improved forecasting can help when a hurricane inevitably makes landfall. The Hurricane HuntersNOAA's G-IV Jet in the forefront and P-3 Aircraft in the back. Image Credit: NOAAWho Are the Hurricane Hunters?In the Atlantic basin (Atlantic Ocean, Gulf of Mexico, and Caribbean Sea) and in the eastern and central Pacific, as required, hurricane reconnaissance is carried out by two government agencies, the U.S. Air Force Reserves’ 53rd Weather Reconnaissance Squadron and NOAA’s Aircraft Operations Center (AOC). The U.S. Navy stopped flying hurricanes in 1974. The 53rd WRS is based at Keesler AFB in Mississippi and maintains a fleet of ten WC-130 planes. These cargo airframes have been modified to carry weather instruments to measure wind, pressure, temperature and dew point as well as drop instrumented sondes and make other observations. AOC is presently based at Linder Airfield in Lakeland, Florida and among its fleet of planes has two P-3 Orions, originally made as Navy sub hunters, but modified to include three radars as well as a suite of meteorological instruments and dropsonde capability. Starting in 1996 AOC added to its fleet a Gulfstream IV jet that is able to make observations from much higher altitudes (up to 45,000 feet). The USAF planes are the workhorses of the hurricane hunting effort. They are often deployed to a forward base, such as Antigua, and carry out most of the reconnaissance of developing waves and depressions. Their mission in these situations is to look for signs of a closed circulation and any strengthening or organizing that the storm might be showing. This information is relayed by satellite to the hurricane specialists who evaluate this information along with data from other platforms. The NOAA planes are more highly instrumented and are primarily used for scientific research on storms, but they may also be called upon for reconnaissance of mature hurricanes when they are threatening landfall, especially on U.S. territory. The planes carry between six to fifteen people, both the flight crew and the weather crew. Flight crews consist of an aircraft commander, co-pilot, flight engineer, navigator, and electrical and data technicians. The weather crew might consist of a flight meteorologist, lead project scientist, cloud physicist, radar scientist, and dropsonde quality scientist. The primary purpose of reconnaissance is to track the center of circulation, these are the co-ordinates that the National Hurricane Center issues, and to measure the maximum winds. But the crews are also evaluating the storm’s size, structure, and development and this information is also relayed to hurricane specialists via satellite link. Most of this data, which is critical in determining the hurricane’s threat, cannot be obtained from satellite. The purposes of research are more varied. Onboard scientists direct the aircraft to those parts of the storm of interest, which might not be near the eye of the hurricane. Experiments might be planned to examine the outer rainbands or the hurricane’s interaction with the environment. The NOAA G-IV jet usually does NOT penetrate the hurricane eye, but is assigned to fly synoptic scale patterns AROUND the storm, deploying dropsondes along the way, in order to profile the environmental flow that is moving the hurricane. In certain circumstances, a USAF WC-130 will also be assigned to fly a similar pattern in coordination with the G-IV to increase the coverage of this synoptic flow mission. Whatever the mission’s purpose, information from all of these flights are shared via satellite with land-based forecasters to keep them current on the storm’s status. Radar and probe data are sent in real-time to be ingested into a variety of computer forecast models to ensure the best quality forecast. Can I Get a Seat on a Hurricane Flight?Sorry, but only people who are part of the mission are allowed on military and public aircraft. This may include accredited members of the press, provided they are working on a current story involving the storm.
Please note that seats are not always available on every flight, and that there is a limit of two seats per media outlet on a given flight. NOAA maintains a lengthy list of requests to fly aboard their aircraft during hurricane missions. If a hurricane is threatening landfall, local media will be given the first opportunity to fly. Due to the dynamics of hurricanes, flight plans can and do change right up until the last minute and flights are often cancelled. All of your contact information (cell numbers, pagers, home/office numbers) is extremely helpful in alerting you to changes. What Is It Like to Fly Into a Hurricane?The most incredible sight that I’ve ever seen is in the middle of a strong hurricane. One might not believe this, but most hurricane flights are fairly boring. They last 10 hours, there are clouds above you and clouds below – so all you see is gray, and you don’t feel the winds swirling around the hurricane. But what does get interesting is flying through the hurricane’s rainbands and the eyewall, which can get a bit turbulent. The eyewall is a donut-like ring of thunderstorms that surround the calm eye. The winds within the eyewall can reach as much as 200 mph [325 km/hr] at the flight level, but you can’t feel these aboard the plane. But what makes flying through the eyewall exhilarating and at times somewhat scary, are the turbulent updrafts and downdrafts that one hits. Those flying in the plane definitely feel these wind currents (they sometimes makes us reach for the air-sickness bags). These vertical winds may reach up to 50 mph [80 km/hr] either up or down, but are actually much weaker in general than what one would encounter flying through a continental supercell thunderstorm. But once the plane gets into the calm eye of a hurricane like Andrew or Gilbert, it is a place of powerful beauty: sunshine streams into the windows of the plane from a perfect circle of blue sky directly above the plane, surrounding the plane on all sides is the blackness of the eyewall’s thunderstorms. Directly below the plane peeking through the low clouds one can see the violent ocean with waves sometimes 60 feet high [20 m] crashing into one another. The partial vacuum of the hurricane’s eye (where one tenth of the atmosphere is gone) is like nothing else on earth. I would much rather experience a hurricane this way – from the safety of a plane – than being on the ground and having the hurricane’s full fury hit without protection. The USAFR 53rd Hurricane Hunters have a ‘cyber flight’ through a hurricane. Visit the page here. Tropical Cyclone ClimatologyDrag the bar to see the impacts of El Niño and its counterpart La Niña on Hurricane Activity. Read more about it in the blog post by Climate.Gov How Many Tropical Cyclones have there been in Each Year in the Atlantic Basin (pre-Satellite Era)?Contributed by Chris Landsea (NHC)
Named Storms = Tropical Storms, Hurricanes and Subtropical Storms References: Landsea, C.W., G.A. Vecchi, L. Bengtsson, and T. R. Knutson, 2010: Impact of Duration Thresholds on Atlantic Tropical Cyclone Counts. Journal of Climate, 23(10), 2508-2519. McAdie, C. J., C. W. Landsea, C. J. Neuman, J. E. David, E. Blake, and G. R. Hamner, 2009: Tropical Cyclones of the North Atlantic Ocean, 1851-2006. Historical Climatology Series 6-2,Prepared by the National Climatic Data Center, Asheville, NC in cooperation with the National Hurricane Center, Miami, FL, 238 pp. Sheets, R.C., 1990: “The National Hurricane Center – Past, present, and future.”, Wea. Forecasting,5, 185-232. Vecchi, G.A. and T. R. Knutson, 2008. “On estimates of historical North Atlantic tropical cyclone activity.”, J. Climate, 21, 3580. How Many Tropical Cyclones have there been in Each Year in the Atlantic Basin (Satellite Era)?Atlantic Basin: Individual years with the numbers in each category
Named Storms = Tropical Storms, Hurricanes and Subtropical Storms References: Landsea, C.W., G.A. Vecchi, L. Bengtsson, and T. R. Knutson, 2010: Impact of Duration Thresholds on Atlantic Tropical Cyclone Counts. Journal of Climate, 23(10), 2508-2519. McAdie, C. J., C. W. Landsea, C. J. Neuman, J. E. David, E. Blake, and G. R. Hamner, 2009: Tropical Cyclones of the North Atlantic Ocean, 1851-2006. Historical Climatology Series 6-2,Prepared by the National Climatic Data Center, Asheville, NC in cooperation with the National Hurricane Center, Miami, FL, 238 pp. Sheets, R.C., 1990: “The National Hurricane Center – Past, present, and future.”, Wea. Forecasting,5, 185-232. Vecchi, G.A. and T. R. Knutson, 2008. “On estimates of historical North Atlantic tropical cyclone activity.”, J. Climate, 21, 3580. Why Do Tropical Cyclones Occur Primarily in the Summer and Autumn?The primary time of year for getting tropical cyclones is during the summer and autumn: July-October for the Northern Hemisphere and December-March for the Southern Hemisphere (though there are differences from basin to basin). The peak in summer/autumn is due to having all of the necessary ingredients become most favorable during this time of year: warm ocean waters (at least 26°C or 80°F), a tropical atmosphere that can quite easily kick off convection (i.e. thunderstorms), low vertical shear in the troposphere, and a substantial amount of large-scale spin available (either through the monsoon trough or easterly waves). While one would intuitively expect tropical cyclones to peak right at the time of maximum solar radiation (late June for the tropical Northern Hemisphere and late December for the tropical Southern Hemisphere), it takes several more weeks for the oceans to reach their warmest temperatures. The atmospheric circulation in the tropics also reaches its most pronounced (and favorable for tropical cyclones) at the same time. This time lag of the tropical ocean and atmospheric circulation is analogous to the daily cycle of surface air temperatures – they are warmest in mid-afternoon, yet the sun’s incident radiation peaks at noon. Why Doesn't the South Atlantic Ocean Experience Tropical Cyclones?What never? Well, hardly ever. In March, 2004 a hurricane DID form in the South Atlantic Ocean and made landfall in Brazil. But this still leaves the question of why hurricanes are so rare in the South Atlantic. Though many people might speculate that the sea surface temperatures are too cold, the primary reasons that the South Atlantic Ocean gets few tropical cyclones are that the tropospheric (near surface to 200mb) vertical wind shear is much too strong and there is typically no inter-tropical convergence zone (ITCZ) over the ocean (Gray 1968). Without an ITCZ to provide synoptic vorticity and convergence (i.e. large scale spin and thunderstorm activity) as well as having strong wind shear, it becomes very difficult to nearly impossible to have genesis of tropical cyclones. In addition, McAdie and Rappaport (1991) documented the occurrence of a strong tropical depression/weak tropical storm that formed off the coast of Congo in mid-April of 1991. This storm lasted about five days and drifted toward the west-southwest into the central South Atlantic. So far, there has not been a systematic study as to the conditions that accompanied this rare event. Why Do Hurricanes Never Hit the West Coast of the United States?Hurricanes form both in the Atlantic basin (i.e. the Atlantic Ocean, Gulf of Mexico and Caribbean Sea) to the east of the continental U.S. and in the Northeast Pacific basin to the west of the U.S. However, the ones in the Northeast Pacific almost never hit the continental U.S., while the ones in the Atlantic basin strike the U.S. mainland just less than twice a year on average. There are two main reasons. The first is that hurricanes tend to move toward the west-northwest after they form in the tropical and subtropical latitudes. In the Atlantic, such a motion often brings the hurricane into the vicinity of the U.S. east coast. In the Northeast Pacific, a west-northwest track takes those hurricanes farther off-shore, well away from the U.S. west coast. In addition to the general track, a second factor is the difference in water temperatures along the U.S. east and west coasts. Along the U.S. east coast, the Gulf Stream provides a source of warm (> 80°F or 26.5°C) waters to help maintain the hurricane. However, along the U.S. west coast, the ocean temperatures rarely get above the lower 70s, even in the midst of summer. Such relatively cool temperatures are not energetic enough to sustain a hurricane’s strength. So for the occasional Northeast Pacific hurricane that does track back toward the U.S. west coast, the cooler waters can quickly reduce the strength of the storm. You may have remnants of such storms move over the Southwestern United States bringing heavy rainfall. Recently Chenoweth and Landsea (2004), re-discovered that a hurricane struck San Diego, California on October 2, 1858. Unprecedented damage was done in the city and was described as the severest gale ever felt to that date nor has it been matched or exceeded in severity since. The hurricane force winds at San Diego are the first and only documented instance of winds of this strength from a tropical cyclone in the recorded history of the state. While climate records are incomplete, 1858 may have been an El Niño year, which would have allowed the hurricane to maintain intensity as it moved north along warmer than usual waters. Today if a Category 1 hurricane made a direct landfall in either San Diego or Los Angeles, damage from such a storm would likely be few to several hundred million dollars. The re-discovery of this storm is relevant to climate change issues and the insurance/emergency management communities risk assessment of rare and extreme events in the region. Reference: Chenoweth, M., and C.W. Lansea (2004): “The San Diego hurricane of October 2, 1858” Bull. Amer. Meteor. Soc., 85, pp.1689-1697 Does an Active June and July Mean the Rest of the Season will be Busy Too?The vast majority of Atlantic activity takes place during August-September-October, the climatological peak months of the hurricane season. The overall number of named storms (hurricanes) occurring in June and July (JJ) correlates at an insignificant r = +0.13 (+0.02) versus the whole season activity. In fact, there is a slight negative relationship between early season storms (hurricanes) versus late season – August through November – r = -0.28 (-0.35). Thus, the overall early season activity, be it very active or quite calm, has little bearing on the season as a whole. These correlations are based on the years 1944-1994. A significant number of pre-season (April-May) and early season (JJ) storms are hybrid systems (neither fully tropical nor midlatitude lows). So their formation mechanisms are very different from fully tropical systems that form in the Main Development Region (MDR). So conditions favoring hybrid storm formation can be very different from those favoring tropical cyclone formation. As shown in (Goldenberg 2000), if one looks only at the June-July Atlantic tropical storms and hurricanes occurring south of 22°N and east of 77°W (the eastern portion of the MDR for Atlantic hurricanes), there is a strong association with activity for the remainder of the year. According to the data from 1944-1999, total overall Atlantic activity for years that had a tropical storm or hurricane form in this region during JJ have been at least average and often above average. So it could be said that a JJ storm in this region is pretty much a “sufficient” (though not “necessary”) condition for a year to produce at least average activity. (I.e., Not all years with average to above-average total overall activity have had a JJ storm in that region, but almost all years with that type of JJ storm produce average to above-average activity.) The formation of a storm in this region during June-July is taken into account when the August updates for the Bill Gray and NOAA seasonal forecasts are issued.
How Does El Niño-Southern Oscillation Affect Tropical Cyclone Activity Around the Globe?The El Niño/Southern Oscillation (ENSO) resolves into a warm phase (El Niño), a cold phase (La Niña), and a neutral phase. During El Niño events (ENSO warm phase), tropospheric vertical shear is increased inhibiting tropical cyclone genesis and intensification, primarily by causing the 200 mb (12 km or 8 mi) westerly winds to be stronger (Gray 1984). La Niña events (ENSO cold phase) enhances activity. Recently, Tang and Neelin (2004) also identified that changes to the moist static stability can also contribute toward hurricane changes due to ENSO, with a drier, more stable environment present during El Niño events. The Australian/Southwest Pacific shows a pronounced shift back and forth of tropical cyclone activity with fewer tropical cyclones between 145° and 165°E and more from 165°E eastward across the South Pacific during El Niño (warm ENSO) events. There is also a smaller tendency to have the tropical cyclones originate a bit closer to the equator. The opposite would be true in La Niña (cold ENSO) events. See papers by Nicholls (1979), Revell and Goulter (1986), Dong (1988), and Nicholls (1992). The western portion of the Northeast Pacific basin (140°W to the dateline) has been suggested to experience more tropical cyclone genesis during the El Niño year and more tropical cyclones tracking into the sub-region in the year following an El Niño (Schroeder and Yu 1995), but this has not been completely documented yet. The Northwest Pacific basin, similar to the Australian/Southwest Pacific basin, experiences a change in location of tropical cyclones without a total change in frequency. Pan (1981), Chan (1985), and Lander (1994) detailed that west of 160°E there were reduced numbers of tropical cyclone genesis with increased formations from 160E to the dateline during El Niño events. The opposite occurred during La Niña events. Again there is also the tendency for the tropical cyclones to also form closer to the equator during El Niño events than average. The eastern portion of the Northeast Pacific, the Southwest Indian, the Southeast Indian/Australian, and the North Indian basins have either shown little or a conflicting ENSO relationship and/or have not been looked at yet in sufficient detail. Reference: Tang, B. H., and J. D. Neelin, 2004: “ENSO Influence on Atlantic hurricanes via tropospheric warming.” Geophys. Res. Lett.: Vol 31, L24204. How Does Atlantic Multi-Decadal Climate Variability Affect Hurricane Activity?There is no debate that hurricane activity is strongly linked to short-term climate swings that last for approximately a year (ENSO) and for tens of years (known as “multi-decadal variability”), but there is an ongoing scientific debate about longer-term climate trends, how much is due to natural phenomena and how much is due to human activities, or how they affect tropical cyclone activity. Atlantic hurricanes respond to the environment that they travel through. For example, when the tropical North Atlantic Ocean is warmer than usual, hurricanes tend to form more often and become stronger. However, when vertical wind shear is higher than normal over the basin, fewer storms form and are weaker. Over the past 100 years and longer, the Atlantic hurricane environment has displayed climate swings known as “multi-decadal variability”, and hurricane activity has followed these swings. For example, in the 1940s through 1960s, ocean temperatures were warmer and hurricane seasons were more active than usual. This situation reversed during the 1970s and 1980s, which was a period of cooler ocean temperature and quieter than usual hurricane seasons. Since around the mid-1990s, we’ve been in another period of warmer than usual ocean temperatures and heightened hurricane activity. Ocean temperatures in the region where most Atlantic hurricanes form and develop have been trending upwards as the Earth has gradually warmed since the mid-19th Century (top panel, Fig. 1). In addition to trending upwards, ocean temperatures show large multi-decadal climate swings from cooler to warmer than average. This becomes clearer when the warming trend is removed (middle panel). Atlantic hurricane activity has responded to these swings in a variety of ways. For example, the number of Atlantic major hurricanes (Saffir-Simpson categories 3–5) is greater during periods of warmer than usual temperatures (bottom panel). Figure 1. Top panel: Atlantic Ocean surface temperature anomalies since 1900. Middle: Top panel with the trend removed to highlight the multi-decadal swings. Bottom: Annual and multi-decadal variation of Atlantic major hurricanes. The average number per year over the past century is about two. Increases in major hurricane counts over the past century may be due entirely or in part to our continually improving ability to measure hurricanes.What Drives Atlantic Multi-decadal Climate Swings?Recent research describes two distinct types of Atlantic climate drivers: 1) Internal variability is caused by natural processes within the atmosphere and ocean climate system. 2) External variability is caused by forces outside of the atmosphere/ocean climate system. Examples of natural internal forces are oceanic oscillations such as ENSO, meridional overturning circulation, and Saharan dust storms that blow mineral dust over the tropical Atlantic. The effects of the El Nino/Southern Oscillation are discussed in another section in detail. Examples of external climate forcing agents are solar variability, cosmic radiation changes, and air pollution such as industrial particulate and sulfur emissions. The Atlantic meridional overturning circulation, which transports ocean heat from the tropics to higher latitudes and can cause substantial climate swings in the Atlantic region and beyond as this circulation increases or decreases. Saharan dust storms have a similar effect on the Atlantic climate as the dust blows westward in the trade-winds off the African continent and blocks sunlight from reaching the ocean surface. Saharan dust storms are strongly seasonal, but can also exhibit multi-decadal swings that can cause similar swings in Atlantic ocean temperatures. Our sun has 11-year and 22-year cycles in sunspot and magnetic activity, which affects the solar wind and Earth’s magnetic field. It may also exhibit longer scale variability in its output. Along with changes in comic ray activity, this may alter Earth’s cloud cover in subtle ways and drive changes in ocean heat content. Volcanic eruptions cause a transient cooling of ocean temperatures as they tend to block some of the incoming sunlight from reaching the surface. These natural eruptions tend to occur randomly and don’t exhibit any clear multi-decadal swings. Finally, there is human-caused particulate and sulfate air pollution, which tends to block incoming sunlight similarly to volcanic eruptions and mineral dust. Human-caused sulfate pollution over the Atlantic exhibits a pronounced variability over time. Prior to the various Clean Air Acts and Amendments instituted by the United States and European countries in the 1970s, industrial sulfate emissions were much less regulated and air quality had become progressively worse. As the concentration of sulfate pollution over the Atlantic Ocean increased from the 1940s through 1970s, a cooling effect was noted as the pollution blocked incoming sunlight. According to some studies, as sulfate pollution concentrations decreased during and after the 1970s, the offsetting cooling effect is believed to have been reduced. How Might Long-Term Climate Change Affect Hurricane Intensity, Frequency, and Rainfall?In November 2006 the global community of tropical cyclone researchers and forecasters as met at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization in San Jose, Costa Rica. They released a statement on the links between anthropogenic (human-induced) climate change and tropical cyclones, including hurricanes and typhoons. The following is a summary of their report.
Consensus Statements by International Workshop on Tropical Cyclones-VI (IWTC-VI) Participants :
A PDF version of the official report is available here. I'm Vacationing in the Caribbean/the Bahamas/Central America/Miami or Elsewhere in the Tropics During Hurricane Season. What Is My Chance of Getting Hit by a Hurricane?Typically, for someone visiting the tropics during June through November, the chance to experience (or even be threatened by) a hurricane is very small. As an example, this figure shows the chances to have a direct hit by a hurricane during the month of September, which is usually the busiest month. If we look at Puerto Rico, the chance is 8% of experiencing a hurricane, if you are there for the WHOLE month. If you are there for, say, only a week, then the chance would be one fourth of that – or only about 2% chance.To put this into perspective, if you made 50 one week trips to Puerto Rico in September, you would only experience a direct hit in ONE of those 50 visits. So the chances to get impacted by a hurricane are quite small for relatively short trips. And the case chosen here is the WORST possible, as all other locations in all other months have smaller chances of being hit by a hurricane. Despite the chance being small, one should know in advance what your hotel’s, cruise company’s, etc. policy is for guests when a hurricane is coming, what actions they plan and what refund policies they have (if any). As is described above, a direct hit by a hurricane is a very rare event for a short visit and if I had a chance – for example – to go on a cruise in the Caribbean Sea during hurricane season, I would go without hesitation. What Is the Average Forward Speed of a Hurricane?The forward speed of hurricanes is very latitude dependent. Typically, Atlantic hurricanes track along the western side of the subtropical ridge in the western Atlantic. As they recurve (turn more northerly) from their westward track they usually slow down. If they reach the midlatitudes, they can interact with upper-level troughs and pick up speed. In the table below, the forward speed of hurricanes in the HURDAT database have been averaged in 5 degree latitude bins : Forward speed of Atlantic hurricanesaveraged by 5 degree latitude bins
While there are many cases where the forward speed over the 6 hour interval in the hurricane database is zero, such as Mitch in 1998, the highest speed in the database is for unnamed Tropical Storm #6 in 1961. As it got caught up by a midlatitude trough over the mid Atlantic states, it went speeding off northeastward over Maine and New Brunswick at a maximum speed of 112.25 km/hr (60.57 kt or 69.75 mph). The fastest hurricane in the record was Emily in 1987, whose maximum speed reached 110.48 km/hr (59.61 kt or 68.65 mph) as it raced over the North Atlantic, before it turned extratropical. Hurricanes in HistoryHistorical Hurricane Tracks at NOAA's Ocean ServiceFor an interactive historical hurricane track map, visit the NOAA Historical Hurricane Tracks tool by NOAA’s Ocean Service. Hurricane HistoryHurricane Timeline 1494-1800
1494- 1800
References: Fitzpatrick, Patrick “Natural Disasters : Hurricanes” 1999 ABC-CLIO Publishers, Santa Barbara, CA Ludlum, David “Early American Hurricanes 1492-1870” 1963 Lancaster Press, Lancaster, PA Simpson, Robert ed. “Hurricane! Coping with Disaster” 2003 American Geophysical Union, Washington, DC Hurricane Timeline 1801-19001801- 1900
References: Fitzpatrick, Patrick “Natural Disasters : Hurricanes” 1999 ABC-CLIO Publishers, Santa Barbara, CA Ludlum, David “Early American Hurricanes 1492-1870” 1963 Lancaster Press, Lancaster, PA Simpson, Robert ed. “Hurricane! Coping with Disaster” 2003 American Geophysical Union, Washington, DC Hurricane Timeline 1901-19501901- 1950
References: Fitzpatrick, Patrick “Natural Disasters : Hurricanes” 1999 ABC-CLIO Publishers, Santa Barbara, CA Ludlum, David “Early American Hurricanes 1492-1870” 1963 Lancaster Press, Lancaster, PA Simpson, Robert ed. “Hurricane! Coping with Disaster” 2003 American Geophysical Union, Washington, DC Hurricane Timeline 1951-20001951-2000
References: Fitzpatrick, Patrick “Natural Disasters : Hurricanes” 1999 ABC-CLIO Publishers, Santa Barbara, CA Ludlum, David “Early American Hurricanes 1492-1870” 1963 Lancaster Press, Lancaster, PA Simpson, Robert ed. “Hurricane! Coping with Disaster” 2003 American Geophysical Union, Washington, DC Hurricane Timeline 2001-20202001-2013
References: Fitzpatrick, Patrick “Natural Disasters : Hurricanes” 1999 ABC-CLIO Publishers, Santa Barbara, CA Ludlum, David “Early American Hurricanes 1492-1870” 1963 Lancaster Press, Lancaster, PA Simpson, Robert ed. “Hurricane! Coping with Disaster” 2003 American Geophysical Union, Washington, DC What Scientific Journals have Regular Articles on Tropical Cyclones?The American Meteorological Society (AMS) publishes the Monthly Weather Review which has annual summaries of Atlantic basin tropical cyclones, Atlantic basin tropical disturbances, and Northeast Pacific (east of 140W) basin tropical cyclones. These summaries have a substantial amount of data and analysis of the storms. Weatherwise prints annual summaries of both the Atlantic and Northeast Pacific basins which are less technical than the Monthly Weather Review articles, but come out months earlier. Mariner’s Weather Log has articles from all of the global basins in annual summaries. These are descriptive and non-technical. For the tropical cyclones of the Southeast Indian/Australia and the Australia/Southwest Pacific basins, Australia’s Bureau of Meteorology publishes Australia Meteorological and Oceanographic Journal has a very thorough annual summary. The Indian journal Mausam carries an annual summary of tropical cyclone activity over the North Indian Ocean. In addition to these summaries, many other AMS journals publish scholarly articles about tropical cyclones, especially the Bulletin of the AMS, Journal of Climate, Journal of Atmospheric Sciences, and Weather and Forecasting. International journals that often carry similar type articles are Geophysical Research Letters, Journal of the Meteorological Society of Japan, Nature, Quarterly Journal of the Royal Meteorological Society,Science, and Weather. What Scientific Books have been Written about Tropical Cyclones?Hurricanes: Their Nature and Impacts on Society Meteorology Today for Scientists and Engineers Global
Perspectives on Tropical Cyclones: From Science to Mitigation Global Guide to Tropical Cyclone Forecasting North
Carolina’s Hurricane History, Florida’s Hurricane History Atlantic Hurricanes Hurricanes, Their Nature and History Into the Hurricane The Divine Wind A Global View of Tropical Cyclones The Hurricane Hurricanes Cyclone Tracy, Picking up the Pieces Beware the Hurricane! Florida Hurricanes and Tropical Storms,
Revised Edition Hurricanes of the North Atlantic Natural Disasters – Hurricanes Tropical Cyclones of the North Atlantic Ocean,
1851-2006 Hurricanes and Florida Agriculture Hurricanes in Novels, Plays & CinemaThere is an undeniable drama to hurricanes; their massive scale affecting the lives of thousands, the foreshadowing of impending doom, and their ponderous pace as they approach the shore. This has made them ideal plot elements in many fictional works. Below is an admittedly partial list of some novels, plays, poems, and movies which have used hurricanes as a major dramatic element. Pre-20th Century
1901-1939
1940-1959
1960-1979
1980-1999
2000-2009
2010-present
Hurricane Records & RanksRecord-Setting Tropical Cyclones
What Are the Record Number of Tropical Storms in a Given Year by Basin?Based on data from 1981-2020
*Note that the data includes subtropical storms in the Atlantic basin numbers. (Neumann 1993)** Note that the data includes storms and hurricanes that formed in the Central Pacific. These values are based on data supplied by the WMO Regional Meteorological Center responsible for tropical cyclone forecasting for that particular basin. Reference: Neumann, C.J. (1993): “Global Overview” – Chapter 1″ Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland Which Hurricanes/ Tropical Storms have Jumped Basins?Here is a list of tropical cyclones that have crossed from the Atlantic basin to the Northeast Pacific and vice versa. To be considered the same tropical cyclone an identifiable center of circulation must be tracked continuously and the cyclone must have been of at least tropical storm strength in both basins (i.e. sustained winds of at least 34 kt, or 18 m/s). This record only goes back to 1923. Before the advent of geostationary satellite pictures in the mid-1960s, the number of Northeast Pacific tropical cyclones was undercounted by a factor of 2 or 3. Thus the lack of many of these events during the 1960s and earlier is mainly due to simply missing the Northeast Pacific TCs. There has not been a recorded case where the same tropical cyclone crossed from the Atlantic into the Northeast Pacific then crossed back into the Atlantic, but Hattie/Simone/Inga in 1961 came close. There is no evidence that a single center of circulation persisted through several crossings of land, but the envelope of moisture and instability from one system helped spawn the next.
Naming Conventions for Basin-Jumping Hurricanes If the system remains a tropical cyclone as it moves across Central America, then it will keep the original name. Only if the tropical cyclone dissipates with just a tropical disturbance remaining, will the hurricane warning center give the system a new name assuming it becomes a tropical cyclone once again in its new basin. What Was the Most (Largest Number) of Hurricanes in the Atlantic Ocean at the Same Time?Four hurricanes occurred simultaneously on two occasions. The first occasion was August 22, 1893, and one of these eventually killed 1,000- 2,000 people in Georgia and South Carolina. The second occurrence was September 25, 1998, when Georges, Ivan, Jeanne and Karl persisted into September 27, 1998 as hurricanes. Georges ended up taking the lives of thousands in Haiti. In 1971 from September 10 to 12, there were five tropical cyclones at the same time; however, while most of these ultimately achieved hurricane intensity, there were never more than two hurricanes at any one time. Reference: Blake, E.S., E.N. Rappaport, J.D. Jarell, and C.W. Landsea, 2005: “The Deadliest, Costliest, and Most Intense United States Hurricanes from 1851 to 2004 (and Other Frequently Requested Hurricane Facts.) NOAA Technical Memorandum NWS-TPC-4, 48 pp. How Many Landfalling Hurricanes have Hit Each State?This table, updated from Jarrell et al. (2001), shows the number of hurricanes affecting the United States and individual states, i.e., direct hits. The table shows that, on the average, close to seven hurricanes every four years (~1.75 per year) strike the United States, while about three major hurricanes cross the U.S. coast every five years (0.60 per year). Other noteworthy facts, updated from Jarrell et al. (2001), are:
Notes: State totals will not equal U.S. totals and Texas and Florida totals will not necessarily equal sum of sectional totals since storms may be counted for more than one state or region. Regional definitions are found in Appendix A of Jarrell et al. (2001). References: Blake, E.S., E.N. Rappaport, J.D. Jarell, and C.W. Landsea, 2005: “The Deadliest, Costliest, and Most Intense United States Hurricanes from 1851 to 2004 (and Other Frequently Requested Hurricane Facts.) NOAA Technical Memorandum NWS-TPC-4, 48 pp. Jarell, J.D., B.M. Mayfield, E.N. Rappaport, and C.W. Landsea, 2001: “The Deadliest, Costliest, and Most Intense United States Hurricanes from 1900 to 2000 (and Other Frequently Requested Hurricane Facts.) NOAA Technical Memorandum NWS-TPC-3, 30 pp. In Which Months Did Major Landfalling Hurricanes Hit Each Coastal State?This table shows the incidence of major hurricanes by months for the U.S. mainland and individual states. September has as many major hurricane landfalls as October and August combined. Texas and Louisiana are the prime targets for pre-August major hurricanes. The threat of major hurricanes increases from west to east during August with major hurricanes favoring the U.S. East Coast by late September. Most major October hurricanes occur in southern Florida (from Blake et al. 2005). Major hurricane direct hits on the U.S. mainland and individual states1851-2020
Note: State totals do not equal U.S. totals. Reference: Blake, E.S., E.N. Rappaport, J.D. Jarell, and C.W. Landsea, 2005: “The Deadliest, Costliest, and Most Intense United States Hurricanes from 1851 to 2004 (and Other Frequently Requested Hurricane Facts.) NOAA Technical Memorandum NWS-TPC-4, 48 pp. How Long Has it Been Since a Hurricane or a Major Hurricane Hit a Given Community in the United States?This table summarizes the occurrence of the last hurricane and major hurricane to directly hit the most populated coastal communities from Brownsville, Texas to Eastport, Maine. In addition, if a hurricane indirectly affected a community after the last direct hit, it is listed in the last column of the table. There are many illustrative examples of the uncertainty of when a hurricane might strike a given locality. After nearly 70 years without a direct hit, Pensacola, Florida was hit directly by Hurricane Erin in 1995 and major Hurricane Ivan in 2004 within 10 years. Miami, which expects a major hurricane every nine years, on average, has been struck only once since 1950 (in 1992). Tampa has not experienced a major hurricane for 84 years. Many locations along the Gulf and Atlantic coasts have not experienced a major hurricane during the period 1851-2018. Last direct or indirect hit by any hurricane or a major hurricane
|
State | City | Last Direct Major Hurricane Hit | Last Direct Hurricane Hit | ||||
Texas | Brownsville | 1980 | Cat3 | Allen | 2020 | Cat1 | Hanna |
Corpus Christi | 1970 | Cat3 | Celia | 1971 | Cat1 | Fern | |
Port Aransas | 2017 | Cat3 | Harvey | 2017 | Cat3 | Harvey | |
Matagorda | 1961 | Cat4 | Carla | 2003 | Cat1 | Claudette | |
Freeport | 1983 | Cat3 | Alicia | 2008 | Cat2 | Ike | |
Galveston | 1983 | Cat3 | Alicia | 2008 | Cat2 | Ike | |
Houston | 2005 | Cat3 | Rita | 2008 | Cat2 | Ike | |
Beaumont | 2005 | Cat3 | Rita | 2007 | Cat1 | Humberto | |
Louisiana | Cameron | 2020 | Cat4 | Laura | 2020 | Cat4 | Laura |
Morgan City | 1992 | Cat3 | Andrew | 2008 | Cat2 | Gustav | |
Houma | 1974 | Cat3 | Carmen | 2020 | Cat2 | Zeta | |
New Orleans | 2005 | Cat3 | Katrina | 2012 | Cat1 | Isaac | |
Mississippi | Bay St. Louis | 2005 | Cat3 | Katrina | 1985 | Cat3 | Elena |
Biloxi | 1985 | Cat3 | Elena | 2017 | Cat1 | Nate | |
Pascagoula | 1985 | Cat3 | Elena | 2005 | Cat1 | Katrina | |
Alabama | Mobile | 1985 | Cat3 | Elena | 2005 | Cat1 | Katrina |
Florida | Pensacola | 2004 | Cat3 | Ivan | 2005 | Cat3 | Dennis |
Panama City | 1995 | Cat3 | Opal | 2005 | Cat1 | Dennis | |
Apalachicola | 2018 | Cat5 | Michael | 2018 | Cat5 | Michael | |
Homosassa | 1950 | Cat3 | Easy | 1968 | Cat2 | Gladys | |
St. Petersburg | 1921 | Cat3 | 1946 | Cat1 | |||
Tampa | 1921 | Cat3 | 1946 | Cat1 | |||
Sarasota | 1944 | Cat3 | 1946 | Cat1 | |||
Fort Myers | 1960 | Cat3 | Donna | 1960 | Cat3 | Donna | |
Naples | 2017 | Cat3 | Irma | 2017 | Cat3 | Irma | |
Key West | 2017 | Cat3 | Irma | 2017 | Cat3 | Irma | |
Miami | 1992 | Cat5 | Andrew | 2005 | Cat1 | Wilma | |
Fort Lauderdale | 1950 | Cat3 | King | 2005 | Cat2 | Wilma | |
W. Palm Beach | 1949 | Cat3 | 2005 | Cat2 | Wilma | ||
Stuart | 2004 | Cat3 | Jeanne | 2004 | Cat3 | Jeanne | |
Fort Pierce | 2004 | Cat3 | Jeanne | 2004 | Cat3 | Jeanne | |
Vero Beach | 2004 | Cat3 | Jeanne | 2004 | Cat3 | Jeanne | |
Cocoa | <1900 | 1995 | Cat1 | Erin | |||
Daytona Bch | <1880 | 1960 | Cat2 | Donna | |||
St. Augustine | <1880 | 1964 | Cat2 | Dora | |||
Jacksonville | <1880 | 1964 | Cat2 | Dora | |||
Fernandina Bch | <1880 | 1928 | Cat2 | ||||
Georgia | Brunswick | 1898 | Cat4 | 1928 | Cat1 | ||
Savannah | 1854 | Cat3 | 1979 | Cat2 | David | ||
S. Carolina | Hilton Head | 1959 | Cat3 | Gracie | 1979 | Cat2 | David |
Charleston | 1989 | Cat4 | Hugo | 2016 | Cat1 | Matthew | |
Myrtle Beach | 1954 | Cat4 | Hazel | 1954 | Cat4 | Hazel | |
N. Carolina | Wilmington | 1996 | Cat3 | Fran | 2018 | Cat1 | Florence |
Morehead City | 1996 | Cat3 | Fran | 1999 | Cat2 | Floyd | |
Cape Hatteras | 1993 | Cat3 | Emily | 2020 | Cat1 | Isaias | |
Virginia | Virginia Beach | 1944 | Cat3 | 2003 | Cat1 | Isabel | |
Norfolk | <1851 | 2003 | Cat1 | Isabel | |||
Maryland | Ocean City | <1851 | <1851 | ||||
Baltimore | <1851 | 1878 | Cat1 | ||||
Delaware | Rehoboth Bch | <1851 | <1851 | ||||
Wilmington | <1851 | 1954 | Cat2 | Hazel | |||
New Jersey | Cape May | <1851 | 1903 | Cat1 | |||
Atlantic City | <1851 | 1903 | Cat1 | ||||
New York | New York City | <1851 | 1903 | Cat1 | |||
Westhampton | 1985 | Cat3 | Gloria | 1985 | Cat3 | Gloria | |
Connecticut | New London | 1938 | Cat3 | 1991 | Cat2 | Bob | |
New Haven | 1938 | Cat3 | 1985 | Cat2 | Gloria | ||
Bridgeport | 1954 | Cat3 | Carol | 1985 | Cat2 | Gloria | |
Rhode Island | Providence | 1954 | Cat3 | Carol | 1991 | Cat2 | Bob |
Mass. | Cape Cod | 1954 | Cat3 | Edna | 1991 | Cat2 | Bob |
Boston | 1869 | Cat3 | 1960 | Cat1 | Donna | ||
New Hampshire | Portsmouth | <1851 | 1985 | Cat2 | Gloria | ||
Maine | Portland | <1851 | 1985 | Cat1 | Gloria | ||
Eastport | <1851 | 1969 | Cat1 | Gerda |
Reference: Blake, E.S., E.N. Rappaport, J.D. Jarell, and C.W. Landsea, 2005: “The Deadliest, Costliest, and Most Intense United States Hurricanes from 1851 to 2004 (and Other Frequently Requested Hurricane Facts.) NOAA Technical Memorandum NWS-TPC-4, 48 pp.
What is the Total Number of Hurricanes and Average Number of Hurricanes in Each Month? When were the Earliest and Latest Hurricanes in a Season?
This table shows the total and average number of tropical storms, and those which became hurricanes, by month, for the period 1851-2020. It also shows the monthly total and average number of hurricanes to strike the U.S. since 1851.
Total and Average Number of Tropical Cyclones by Month(1851-2020)
Month | Tropical Storms | Hurricanes | U.S. Landfalling Hurricanes | |||
Total | Average | Total | Average | Total | Average | |
JANUARY | 5 | * | 3 | * | 0 | * |
FEBRUARY | 1 | * | 0 | * | 0 | * |
MARCH | 1 | * | 1 | * | 0 | * |
APRIL | 2 | * | 0 | * | 0 | * |
MAY | 27 | 0.2 | 4 | * | 0 | * |
JUNE | 98 | 0.6 | 33 | 0.2 | 19 | 0.11 |
JULY | 133 | 0.8 | 61 | 0.4 | 28 | 0.16 |
AUGUST | 403 | 2.6 | 248 | 1.6 | 81 | 0.48 |
SEPTEMBER | 634 | 4.0 | 414 | 2.6 | 110 | 0.65 |
OCTOBER | 370 | 2.3 | 217 | 1.4 | 60 | 0.36 |
NOVEMBER | 106 | 0.7 | 50 | 0.3 | 3 | 0.02 |
DECEMBER | 20 | 0.1 | 7 | * | 0 | * |
YEAR | 1800 | 11.4 | 1038 | 6.6 | 301 | 1.78 |
* Less than 0.05.
Excludes subtropical storms
The hurricane season is defined as June 1 through November 30. An early hurricane can be defined as occurring in the three months prior to the start of the season, and a late hurricane can be defined as occurring in the three months after the season. With these criteria the earliest observed hurricane in the Atlantic was on January 4 1938, while the latest observed hurricane was on December 31, 1954, the second ‘Alice’ of that year which persisted as a hurricane until January 5, 1955.
The earliest hurricane to strike the United States was Alma which struck northwest Florida on June 9, 1966. The latest hurricane to strike the U. S. was Kate on November 22, 1985 near Mexico Beach, Florida.
Which Countries have had the Most Tropical Cyclones Hits?
This table ranks the top ten countries by most tropical cyclone strikes. These numbers are approximated from the IBTrACS database and include only those storm tracks that intersected the coastline at hurricane intensity (≥ 65 kt) and does NOT include storms that remained just offshore but may have affected the country.
Total number of tropical cyclone hits by countryRank | Nation | Hits |
1 | United States of America | 268 |
2 | China | 230 |
3 | Philippines | 176 |
4 | Mexico | 134 |
5 | Japan | 133 |
6 | Cuba | 79 |
7 | Australia | 66 |
8 | Bahamas | 61 |
9 | Vietnam | 45 |
10 | Madagascar | 30 |
However, it should be noted that some basins have longer histories of such activity and this might bias these counts. So the following is the ranking if we only look at storms since 1970, when world-wide satellite coverage became available.
Ranking of tropical cyclone hits by countrysince 1970
Rank | Nation |
1 | China |
2 | Philippines |
3 | Japan |
4 | Mexico |
5 | United States of America |
6 | Australia |
7 | Taiwan |
8 | Vietnam |
9 | Madagascar |
10 | Cuba |
When was the earliest and latest Atlantic hurricane?
Year | Name | Record Type | Attribution |
---|---|---|---|
1908 | Unnamed | Earliest Hurricane in the Season | Earliest observed hurricane for the season in the Atlantic was on March 7, 1908 |
1954 | Hurricane Alice | Latest Hurricane in the Season | December 31, 1954, the second ‘Alice’ of that year which persisted as a hurricane until January 5, 1955. |
1966 | Alma | Earliest Hurricane landfall in the United States | Northwest Florida on June 9, 1966 |
1985 | Kate | Latest Hurricane landfall in the United States | November 22, 1985 near Mexico Beach, Florida |
What have been the Costliest Tropical Cyclones in the United States?
Costliest mainland United States tropical cyclones 1900-2017
Unadjusted for inflation
RANK | TROPICAL CYCLONE | YEAR | CATEGORY | DAMAGE (U.S.$) |
1 | KATRINA (SE FL, LA, MS) | 2005 | 3 | $125,000,000,000 |
1 | HARVEY (TX, LA) | 2017 | 4 | 125,000,000,000 |
4 | SANDY(Mid-Atlantic & NE US) (Post-Tropical at landfall) | 2012 | 1 | 65,000,000,000 |
5 | IRMA (FL) | 2017 | 4 | 50,000,000,000 |
6 | IKE (TX, LA) | 2008 | 2 | 30,000,000,000 |
7 | ANDREW (SE FL/LA) | 1992 | 5 | 27,000,000,000 |
8 | IVAN (AL/NW FL) | 2004 | 3 | 20,500,000,000 |
9 | WILMA (S FL) | 2005 | 3 | 19,000,000,000 |
10 | RITA (SW LA, N TX) | 2005 | 3 | 18,500,000,000 |
11 | CHARLEY (SW FL) | 2004 | 4 | 16,000,000,000 |
12 | IRENE(Mid-Atlantic & NE US) | 2011 | 1 | 13,500,000,000 |
13 | MATTHEW (SE US) | 2016 | 1 | 10,000,000,000 |
14 | FRANCES (FL) | 2004 | 2 | 9,800,000,000 |
15 | ALLISON (N TX) Tropical Storm | 2001 | TS | 8,500,000,000 |
16 | JEANNE (FL) | 2004 | 3 | 7,500,000,000 |
17 | HUGO (SC) | 1989 | 4 | 7,000,000,000 |
18 | FLOYD (Mid-Atlantic & NE U.S.) | 1999 | 2 | 6,500,000,000 |
19 | GUSTAV (LA) | 2008 | 2 | 6,000,000,000 |
20 | ISABEL (Mid-Atlantic) | 2003 | 2 | 5,500,000,000 |
21 | FRAN (NC) | 1996 | 3 | 5,000,000,000 |
22 | OPAL (NW FL) | 1995 | 3 | 4,700,000,000 |
25 | ALICIA (N TX) | 1983 | 3 | 3,000,000,000 |
26 | ISAAC (LA) | 2012 | 1 | 2,800,000,000 |
27 | GEORGES (FL Keys, MS, AL) | 1998 | 2 | 2,500,000,000 |
27 | DENNIS (NW FL) | 2005 | 3 | 2,500,000,000 |
29 | AGNES (FL/NE U.S.) | 1972 | 1 | 2,100,000,000 |
32 | FREDERIC (AL/MS) | 1979 | 3 | 1,700,000,000 |
33 | BOB (NC, NE U.S) | 1991 | 2 | 1,500,000,000 |
33 | JUAN (LA) | 1985 | 1 | 1,500,000,000 |
35 | CAMILLE (MS/SE LA/VA) | 1969 | 5 | 1,420,700,000 |
36 | BETSY (SE FL/SE LA) | 1965 | 3 | 1,420,500,000 |
37 | ELENA (MS/AL/NW FL) | 1985 | 3 | 1,300,000,000 |
37 | DOLLY (S TX) | 2008 | 1 | 1,300,000,000 |
39 | LILI (SC LA) | 2002 | 1 | 1,100,000,000 |
40 | ALBERTO (AL, GA) Tropical Storm | 1994 | TS | 1,030,000,000 |
41 | BONNIE (Mid-Atlantic) | 1998 | 2 | 1,000,000,000 |
ADDENDUM Non-CONUS tropical cyclone damage (Rank is independent of other events in group) | ||||
3 | MARIA (PR, USVI) | 2017 | 4 | 90,000,000,000 |
23 | GEORGES (USVI,PR) | 1998 | 3 | 3,500,000,000 |
24 | INIKI (Kauai, HI) | 1992 | 4 | 3,100,000,000 |
29 | MARILYN (USVI, PR) | 1995 | 2 | 2,100,000,000 |
31 | HUGO (USVI, PR) | 1989 | 4 | 2,000,000,000 |
The thirty costliest mainland United States tropical cyclones 1900-2017
Adjusted to 2017 US $s
RANK | HURRICANE | YEAR | CATEGORY | DAMAGE (U.S. $) |
1 | KATRINA (SE FL, LA, MS) | 2005 | 3 | $160,000,000,000 |
2 | HARVEY (TX, LA) | 2017 | 4 | $125,000,000,000 |
4 | SANDY(Mid-Atlantic & NE US) Post-Tropical at landfall | 2012 | 1 | 70,200,000,000 |
5 | IRMA (FL) | 2017 | 4 | 50,000,000,000 |
6 | ANDREW (SE FL/LA) | 1992 | 5 | 47,790,000,000 |
7 | IKE (TX, LA) | 2008 | 2 | 34,800,000,000 |
8 | IVAN (AL/NW FL) | 2004 | 3 | 27,060,000,000 |
9 | WILMA (S FL) | 2005 | 3 | 24,320,000,000 |
10 | RITA (SW LA, N TX) | 2005 | 3 | 23,680,000,000 |
11 | CHARLEY (SW FL) | 2004 | 4 | 21,120,000,000 |
12 | IRENE(Mid-Atlantic & NE US) | 2011 | 1 | 14,985,000,000 |
13 | HUGO (SC) | 1989 | 4 | 14,070,000,000 |
14 | FRANCES (FL) | 2004 | 2 | 12,936,000,000 |
15 | AGNES (FL/NE U.S.) | 1972 | 1 | 12,516,000,000 |
16 | ALLISON (N TX) Tropical Storm | 2001 | TS | 11,815,000,000 |
17 | BETSY (SE FL/SE LA) | 1965 | 3 | 11,152,000,000 |
18 | MATTHEW (SE US) | 2016 | 1 | 10,300,000,000 |
19 | JEANNE (FL) | 2004 | 3 | 9,900,000,000 |
20 | CAMILLE (MS/SE LA/VA) | 1969 | 5 | 9,776,000,000 |
21 | FLOYD (Mid-Atlantic & NE U.S.) | 1999 | 2 | 9,620,000,000 |
22 | FRAN (NC) | 1996 | 3 | 7,900,000,000 |
23 | DIANE (NC) | 1955 | 1 | 7,630,000,000 |
24 | OPAL (NW FL) | 1995 | 3 | 7,614,000,000 |
25 | ALICIA (N TX) | 1983 | 3 | 7,470,000,000 |
26 | ISABEL (Mid-Atlantic) | 2003 | 2 | 7,370,000,000 |
27 | GUSTAV (LA) | 2008 | 2 | 6,960,000,000 |
28 | CELIA (TX) | 1970 | 3 | 6,026,000,000 |
29 | FREDERIC (AL/MS) | 1979 | 3 | 5,712,000,000 |
32 | LONG ISLAND EXPRESS (NE US) | 1938 | 3 | 5,279,000,000 |
33 | NC/VA 1944 (Mid-Atlantic) | 1944 | 3 | 4,927,000,000 |
34 | CAROL (NE US) | 1954 | 3 | 4,198,000,000 |
36 | GEORGES (FL Keys, MS, AL) | 1998 | 2 | 3,775,000,000 |
38 | DONNA (FL, Eastern US) | 1960 | 4 | 3,235,000,000 |
39 | DENNIS (NW FL) | 2005 | 3 | 3,200,000,000 |
40 | ISAAC (LA) | 2012 | 1 | 3,024,000,000 |
41 | ELENA (MS/AL/NW FL) | 1985 | 3 | 3,003,000,000 |
ADDENDUM Non-CONUS tropical cyclone damage (Rank is independent of other events in group) | ||||
3 | MARIA (PR, USVI) | 2017 | 4 | 90,000,000,000 |
30 | INIKI (Kauai, HI) | 1992 | 4 | 5,487,000,000 |
31 | GEORGES (USVI,PR) | 1998 | 3 | 5,285,000,000 |
35 | HUGO (USVI, PR) | 1989 | 4 | 4,020,000,000 |
37 | MARILYN (USVI, PR) | 1995 | 2 | 3,402,000,000 |
What have been the Most Intense Hurricanes to Strike the United States?
The most intense mainland United States hurricanes by central pressure (1851-2018)
RANK | HURRICANE | YEAR | CATEGORY (at landfall) | MINIMUM PRESSURE | |
Millibars | Inches | ||||
1 | FL (Keys) | 1935 | 5 | 892 | 26.35 |
2 | CAMILLE (MS/SE LA/VA) | 1969 | 5 | 900 | 26.58 |
3 | MICHAEL (NW FL) | 2018 | 5 | 920 | 27.17 |
4 | KATRINA (LA) | 2005 | 3 | 920 | 27.17 |
5 | ANDREW (SE FL/SE LA) | 1992 | 5 | 922 | 27.23 |
6 | TX (Indianola) | 1886 | 4 | 925 | 27.31 |
7 | FL (Keys)/S TX | 1919 | 4 | 927 | 27.37 |
8 | FL (Lake Okeechobee) | 1928 | 4 | 929 | 27.43 |
9 | DONNA (FL/Eastern U.S.) | 1960 | 4 | 930 | 27.46 |
10 | LA (New Orleans) | 1915 | 4 | 931 | 27.49 |
CARLA (N & Central TX) | 1961 | 4 | 931 | 27.49 | |
12 | LA (Last Island) | 1856 | 4 | 934 | 27.58 |
13 | HUGO (SC) | 1989 | 4 | 934 | 27.58 |
14 | FL (Miami)/MS/AL/Pensacola | 1926 | 4 | 935 | 27.61 |
15 | TX (Galveston) | 1900 | 4 | 936 | 27.64 |
16 | RITA (NE TX,W LA) | 2005 | 3 | 937 | 27.67 |
17 | GA/FL (Brunswick) | 1898 | 4 | 938 | 27.70 |
18 | HAZEL (SC/NC) | 1954 | 4 | 938 | 27.70 |
19 | SE FL/SE LA/MS | 1947 | 4 | 940 | 27.76 |
20 | N TX | 1932 | 4 | 941 | 27.79 |
CHARLEY (SW FL) | 2004 | 4 | 941 | 27.79 | |
22 | GLORIA (Eastern U.S.) | 1985 | 3& | 942 | 27.82 |
OPAL (NW FL/AL) | 1995 | 3& | 942 | 27.82 | |
— | SANDY (NJ/NY/CN) | 2012 | 1% | 942 | 27.82 |
24 | FL (Central) | 1888 | 3 | 945 | 27.91 |
E NC | 1899 | 3 | 945 | 27.91 | |
AUDREY (SW LA/N TX) | 1957 | 4# | 945 | 27.91 | |
TX (Galveston) | 1915 | 4# | 945 | 27.91 | |
CELIA (S TX) | 1970 | 3 | 945 | 27.91 | |
ALLEN (S TX) | 1980 | 3 | 945 | 27.91 | |
30 | New England | 1938 | 3 | 946 | 27.94 |
FREDERIC (AL/MS) | 1979 | 3 | 946 | 27.94 | |
IVAN (AL, NW FL) | 2004 | 3 | 946 | 27.94 | |
DENNIS (NW FL) | 2005 | 3 | 946 | 27.94 | |
34 | NE U.S. | 1944 | 3 | 947 | 27.97 |
SC/NC | 1906 | 3 | 947 | 27.97 | |
36 | LA (Chenier Caminanda) | 1893 | 3 | 948 | 27.99 |
36 | BETSY (SE FL/SE LA) | 1965 | 3 | 948 | 27.99 |
SE FL/NW FL | 1929 | 3 | 948 | 27.99 | |
SE FL | 1933 | 3 | 948 | 27.99 | |
S TX | 1916 | 3 | 948 | 27.99 | |
MS/AL | 1916 | 3 | 948 | 27.99 | |
42 | NW FL | 1882 | 3 | 949 | 28.02 |
DIANA (NC) | 1984 | 3+ | 949 | 28.02 | |
S TX | 1933 | 3 | 949 | 28.02 | |
45 | WILMA (SW FL) | 2005 | 3 | 950 | 28.05 |
GA/SC | 1854 | 3 | 950 | 28.05 | |
LA/MS | 1855 | 3 | 950 | 28.05 | |
LA/MS/AL | 1860 | 3 | 950 | 28.05 | |
LA | 1879 | 3 | 950 | 28.05 | |
BEULAH (S TX) | 1967 | 3 | 950 | 28.05 | |
HILDA (Central LA) | 1964 | 3 | 950 | 28.05 | |
GRACIE (SC) | 1959 | 3 | 950 | 28.05 | |
TX (Central) | 1942 | 3 | 950 | 28.05 | |
JEANNE (FL) | 2004 | 3 | 950 | 28.05 | |
IKE (TX/LA) | 2008 | 2 | 950 | 28.05 | |
55 | SE FL | 1945 | 3 | 951 | 28.08 |
BRET (S TX) | 1999 | 3 | 951 | 28.08 | |
57 | LA (Grand Isle) | 1909 | 3 | 952 | 28.11 |
FL (Tampa Bay) | 1921 | 3 | 952 | 28.11 | |
CARMEN (Central LA) | 1974 | 3 | 952 | 28.11 | |
IRENE (NC) | 2011 | 1 | 952 | 28.11 | |
SC/NC | 1885 | 3 | 953 | 28.14 | |
S FL | 1906 | 3 | 953 | 28.14 | |
62 | GA/SC | 1893 | 3 | 954 | 28.17 |
EDNA (New England) | 1954 | 3 | 954 | 28.17 | |
SE FL | 1949 | 3 | 954 | 28.17 | |
FRAN (NC) | 1996 | 3 | 954 | 28.17 | |
GUSTAV (LA) | 2008 | 2 | 954 | 28.17 | |
66 | SE FL | 1871 | 3 | 955 | 28.20 |
LA/TX | 1886 | 3 | 955 | 28.20 | |
SC/NC | 1893 | 3 | 955 | 28.20 | |
NW FL | 1894 | 3 | 955 | 28.20 | |
ELOISE (NW FL) | 1975 | 3 | 955 | 28.20 | |
KING (SE FL) | 1950 | 3 | 955 | 28.20 | |
Central LA | 1926 | 3 | 955 | 28.20 | |
SW LA | 1918 | 3 | 955 | 28.20 |
Notes:
Includes only major hurricanes at their most intense landfall.
&Highest category justified by winds.
#Classified 4 because of estimated winds.
+Cape Fear, NC area only; was a category 2 at final landfall.
%Storm post-tropical at landfall
non-CONUS storms
RANK | HURRICANE | YEAR | CATEGORY (at landfall) | MINIMUM PRESSURE | |
Millibars | Inches | ||||
4 | DAVID (S of PR) | 1979 | 4 | 924 | 27.29 |
9 | San Felipe (PR) | 1928 | 5 | 931 | 27.49 |
18 | HUGO (USVI & PR) | 1989 | 4 | 940 | 27.76 |
44 | INIKI (KAUAI, HI) | 1992 | UNK | 950 | 27.91 |
65 | DOT (KAUAI, HI) | 1959 | UNK | 955 | 28.11 |
What have been the Deadliest Hurricanes for the United States?
RANK | HURRICANE | YEAR | CAT | DEATHS | COMMENTS |
1 | TX (Galveston) | 1900 | 4 | 8000-12,000 | |
2 | FL (SE/Lake Okeechobee) | 1928 | 4 | 2500-3000 | Same storm as #13 ADDENDUM |
3 | KATRINA (LA,MS,AL,FL,GA) | 2005 | 3 | 1500 | Deaths directly attributed |
4 | LA (Cheniere Caminanda) | 1893 | 4 | 1100-1400 | 2000 including offshore deaths August |
5 | SC/GA (Sea Islands) | 1893 | 3 | 1000-2000 | |
6 | GA/SC | 1881 | 2 | 700 | |
7 | AUDREY (SW LA/N TX) | 1957 | 4 | >416 | |
8 | FL (Keys) | 1935 | 5 | 408 | |
9 | LA (Last Island) | 1856 | 4 | 400 | With offshore deaths total is ~600 |
10 | FL (Miami)/MS/AL/Pensacola | 1926 | 4 | 372 | |
11 | LA (Grand Isle) | 1909 | 3 | 350 | |
12 | FL (Keys)/S TX | 1919 | 4 | 287 | With offshore deaths total is ~600 |
13 | LA (New Orleans) | 1915 | 4 | 275 | |
14 | TX (Galveston) | 1915 | 4 | 275 | |
15 | New England | 1938 | 3 | 256 | With offshore deaths total is ~600 |
16 | CAMILLE (MS/SE LA/VA) | 1969 | 5 | 256 | |
17 | DIANE (NE U.S.) | 1955 | 1 | 184 | |
18 | GA, SC, NC | 1898 | 4 | 179 | |
19 | TX | 1875 | 3 | 176 | |
20 | SE FL | 1906 | 3 | 164 | |
21 | TX (Indianola) | 1886 | 4 | 150 | |
22 | MS/AL/Pensacola | 1906 | 2 | 134 | |
23 | FL, GA, SC | 1896 | 3 | 130 | |
24 | AGNES (FL/NE U.S.) | 1972 | 1 | ≤122 | |
25 | HAZEL (SC/NC) | 1954 | 4 | 95 | |
26 | BETSY (SE FL/SE LA) | 1965 | 3 | 75 | |
** | SANDY (NJ,NY,CN) | 2012 | – | 72 | |
27 | Northeast U.S. | 1944 | 3 | 64 | Total 390 with offshore deaths |
28 | CAROL (NE U.S.) | 1954 | 3 | 60 | |
29 | FLOYD (Mid Atlantic & NE U.S.) | 1999 | 2 | 56 | |
30 | NC | 1883 | 2 | 53 | |
31 | SE FL/SE LA/MS | 1947 | 4 | 51 | |
32 | NC, SC | 1899 | 3 | ≥50 | Same storm as #2 in ADDENDUM |
32 | GA/SC/NC | 1940 | 2 | 50 | |
32 | DONNA (FL/Eastern U.S.) | 1960 | 4 | 50 | |
35 | LA | 1860 | 2 | ≥47 | |
36 | IRENE NC/VA/NE | 2011 | 1 | 47 | |
37 | NC, VA | 1879 | 3 | ≥46 | Could include offshore deaths |
38 | CARLA (N & Central TX) | 1961 | 4 | 46 | |
39 | TX (Velasco) | 1909 | 3 | 41 | |
40 | ALLISON (SE TX) | 2001 | TS | 41 | |
41 | Mid-Atlantic | 1889 | unk | ≥40 | Could include offshore deaths Storm remained offshore |
41 | TX (Freeport) | 1932 | 4 | 40 | |
41 | S TX | 1933 | 3 | 40 | |
44 | HILDA (LA) | 1964 | 3 | 38 | |
45 | SW LA | 1918 | 3 | 34 | |
46 | SW FL | 1910 | 3 | 30 | |
47 | ALBERTO (NW FL, GA, AL) | 1994 | TS | 30 | |
48 | SC, FL | 1893 | 3 | 28 | Mid-October |
49 | New England | 1878 | 2 | ≥27 | |
50 | Texas | 1886 | 2 | ≥27 | |
ADDENDUM (Not Atlantic/Gulf Coast) | |||||
2 | Puerto Rico | 1899 | 3 | 3369 | Same storm as #32 |
5 | P.R. USVI | 1867 | 3 | ≤811 | Could include offshore deaths |
5 | Puerto Rico | 1852 | 1 | ≤800 | Total possibly from 2 storms |
13 | Puerto Rico (San Felipe) | 1928 | 5 | 312 | Same storm as #2 |
17 | USVI, Puerto Rico | 1932 | 2 | 225 | |
25 | DONNA (St. Thomas, VI) | 1960 | 4 | 107 | |
25 | Puerto Rico | 1888 | 1 | ≥100 | |
37 | Southern California | 1939 | TS | 45 | |
37 | ELOISE(Puerto Rico) | 1975 | TS | 44 | |
47 | USVI | 1871 | 3 | ≥27 |
** SANDY 2012 was not classified a tropical cyclone when it came ashore but is placed in this table for reference relative to other storms.
Reference: The Deadliest, Costliest, and Most Intense United States Tropical Cyclones from 1851 to 2006 (and other Frequently Requested Hurricane Facts) NOAA Technical Memorandum NWS TPC-5 April 15, 2007, Eric S. Blake, Edward N. Rappaport, Christopher W. Landsea.
What were the Deadliest Years for Hurricanes in the United States?
This table ranks the top 30 years by deaths, by unadjusted damage and by adjusted damage. In most years the death and damage totals are the result of a single, major hurricane.
The Thirty Deadliest and Costliest YearsRanked on Deaths (1851-2015) | Ranked on Unadjusted Damage (1900-2015) | Ranked on Adjusted Damage (1900-2013) | Ranked by Normalized Damage (1900-2004) | ||||||||
Rank | Year | Deaths | Rank | Year | $ Millions | Rank | Year | $ Millions | Rank | Year | $ Millions |
1 | 1900 | 8,0001 | 1 | 2005 | 120,000 | 1 | 2005 | 120,000 | 1 | 1926 | 104,908 |
2 | 1893 | ~3,0002 | 2 | 2012 | 73,550 | 2 | 2012 | 62,564 | 2 | 2004 | 45,000 |
3 | 1928 | 2,500 | 3 | 2004 | 45,000 | 3 | 2004 | 46,337 | 3 | 1992 | 43,152 |
4 | 2005 | 2,067 | 4 | 1992 | 26,500 | 4 | 1992 | 35,993 | 4 | 1900 | 37,541 |
5 | 1881 | 700 | 5 | 2008 | 23,370 | 5 | 2008 | 21,198 | 5 | 1915 | 33,344 |
6 | 1915 | 550 | 6 | 2011 | 15,800 | 6 | 2011 | 13,720 | 6 | 1944 | 33,1334 |
7 | 1935 | 414 | 7 | 1989 | 7,670 | 7 | 1989 | 10,991 | 7 | 1938 | 23,464 |
8 | 1926 | 408 | 8 | 1999 | 5,532 | 8 | 1965 | 8,921 | 8 | 1954 | 22,844 |
9 | 1909 | 406 | 9 | 2001 | 5,260 | 9 | 1972 | 8,858 | 9 | 1928 | 19,457 |
10 | 1957 | 400 | 10 | 1998 | 4,344 | 10 | 1969 | 7,202 | 10 | 1955 | 17,204 |
11 | 1906 | 298 | 11 | 1985 | 4,000 | 11 | 1979 | 6,769 | 11 | 1965 | 16,557 |
12 | 1919 | 287 | 12 | 1995 | 3,723 | 12 | 1955 | 6,757 | 12 | 1960 | 15,918 |
12 | 1969 | 256 | 13 | 1996 | 3,600 | 13 | 1985 | 6,642 | 13 | 1947 | 15,196 |
14 | 1938 | 256 | 14 | 2003 | 3,600 | 14 | 2001 | 6,314 | 14 | 1969 | 14,298 |
15 | 1955 | 218 | 15 | 1979 | 3,045 | 15 | 1938 | 6,148 | 15 | 1972 | 13,978 |
16 | 1954 | 193 | 16 | 1972 | 2,100 | 16 | 1998 | 5,990 | 16 | 1989 | 13,436 |
17 | 1972 | 122 | 17 | 1983 | 2,000 | 17 | 1999 | 5,907 | 17 | 1979 | 11,264 |
18 | 1916 | 107 | 18 | 1991 | 1,500 | 18 | 1954 | 5,293 | 18 | 1945 | 9,958 |
19 | 2012 | 86 | 19 | 1965 | 1,445 | 19 | 1995 | 4,499 | 19 | 1903 | 9,730 |
20 | 1965 | 75 | 20 | 1969 | 1,421 | 20 | 1996 | 4,252 | 20 | 1961 | 9,340 |
21 | 1960 | 65 | 21 | 2002 | 1,220 | 21 | 2003 | 4,008 | 21 | 1964 | 9,193 |
22 | 1944 | 64 | 22 | 1955 | 985 | 22 | 1983 | 3,523 | 22 | 1949 | 8,707 |
23 | 1933 | 63 | 23 | 1994 | 973 | 23 | 1964 | 3,268 | 23 | 1985 | 8,567 |
24 | 1999 | 62 | 24 | 1954 | 756 | 24 | 1915 | 2,6693 | 24 | 1919 | 7,543 |
25 | 2004 | 60 | 25 | 1964 | 515 | 25 | 1961 | 2,665 | 25 | 2001 | 6,254 |
26 | 1989 | 56 | 26 | 1975 | 490 | 26 | 1944 | 2,6144 | 26 | 1999 | 6,222 |
27 | 1966 | 54 | 27 | 1970 | 454 | 27 | 1960 | 2,537 | 27 | 1906 | 5,739 |
28 | 1947 | 53 | 28 | 1961 | 414 | 28 | 1926 | 2,250 | 28 | 1998 | 5,484 |
29 | 2011 | 52 | 29 | 1960 | 396 | 29 | 1970 | 2,171 | 29 | 1983 | 5,289 |
30 | 1940 | 51 | 30 | 1938 | 306 | 30 | 1991 | 2,064 | 30 | 1916 | 5,077 |
Notes:
Adjusted – Adjusted to 2005 dollars based on U.S. Department of Commerce Implicit Price Deflator for Construction.
Normalized – Landsea normalization reflects inflation, changes in personal wealth and coastal county population to 2004 (Pielke and Landsea 1998.)
1 Could have been as high as 12,000.
2 Considered too high in 1915 reference.
3 Using 1915 cost adjustment –
none available prior to 1915.
4 Could include offshore losses.
What is the Total United States Damage and Death Toll for Each Year Since 1900?
Estimated annual deaths and damages
Year | Deaths | Damage ($ Millions) | ||
Unadjusted | Adjusted | Normalized | ||
1900 | 8,000 | 301 | 1,271 2 | 37,541 |
1901 | 10 | 1 | 42 2 | 904 |
1902 | 0 | Minor | Minor | 0 |
1903 | 15 | 1 | 42 2 | 9,730 |
1904 | 5 | 2 | 84 2 | 1,177 |
1905 | 0 | Minor | Minor | 0 |
1906 | 298 | 3 | + 127 2 | 5,739 |
1907 | 0 | Minor | Minor | 0 |
1908 | 0 | Minor | Minor | 0 |
1909 | 406 | 8 | 339 2 | 4,121 |
1910 | 30 | 1 | 42 2 | 1,591 |
1911 | 17 | 1 | + 42 2 | 304 |
1912 | 1 | Minor | Minor | 0 |
1913 | 5 | 3 | 127 2 | 920 |
1914 | 0 | Minor | Minor | 0 |
1915 | 550 | 63 | 2,669 3 | 33,344 |
1916 | 107 | 33 | 1,148 | 5,077 |
1917 | 5 | Minor | Minor | 0 |
1918 | 34 | 5 | 113 | 516 |
1919 | 287 | 22 | 447 | 7,543 |
1920 | 2 | 3 | 48 | 514 |
1921 | 6 | 3 | 61 | 4,584 |
1922 | 0 | Minor | Minor | 0 |
1923 | 0 | Minor | Minor | 0 |
1924 | 2 | Minor | Minor | 0 |
1925 | 6 | Minor | Minor | 0 |
1926 | 408 | 112 | 2,250 | 104,908 |
1927 | 0 | Minor | Minor | 0 |
1928 | 2,500 | 25 | 502 | 19,457 |
1929 | 3 | 1 | 18 | 190 |
1930 | 0 | Minor | Minor | 0 |
1931 | 0 | Minor | Minor | 0 |
1932 | 40 | 8 | 171 | 2,558 |
1933 | 63 | 47 | 1,117 | 4,892 |
1934 | 17 | 5 | 108 | 517 |
1935 | 414 | 12 | 259 | 4,469 |
1936 | 9 | 2 | 45 | 146 |
1937 | 0 | Minor | Minor | 0 |
1938 | 600 | 306 | 6,148 | 23,464 |
1939 | 3 | Minor | Minor | 0 |
1940 | 51 | 5 | 105 | 722 |
1941 | 10 | 8 | 155 | 1,410 |
1942 | 8 | 27 | 457 | 1,647 |
1943 | 16 | 17 | 270 | 2,131 |
1944 | 64 | 165 | 2,614 | 33,133 |
1945 | 7 | 80 | 1,237 | 9,958 |
1946 | 0 | 5 | 66 | 3,162 |
1947 | 53 | 136 | 1,497 | 15,196 |
1948 | 3 | 18 | 180 | 2,383 |
1949 | 4 | 59 | 590 | 8,707 |
1950 | 19 | 36 | 354 | 3,958 |
1951 | 0 | 2 | 17 | 256 |
1952 | 3 | 3 | 21 | 82 |
1953 | 2 | 6 | 42 | 37 |
1954 | 193 | 756 | 5,293 | 22,844 |
1955 | 218 | 985 | 6,757 | 17,204 |
1956 | 19 | 27 | 175 | 456 |
1957 | 400 | 152 | 960 | 3,186 |
1958 | 2 | 11 | 69 | 290 |
1959 | 24 | 23 | 147 | 582 |
1960 | 65 | 396 | 2,537 | 15,918 |
1961 | 46 | 414 | 2,664 | 9,340 |
1962 | 3 | 2 | 12 | 55 |
1963 | 10 | 12 | 75 | 194 |
1964 | 49 | 515 | 3,268 | 9,193 |
1965 | 75 | 1,445 | 8,921 | 16,557 |
1966 | 54 | 15 | 88 | 215 |
1967 | 18 | 200 | 1,146 | 2,673 |
1968 | 9 | 10 | 54 | 417 |
1969 | 256 | 1,421 | 7,201 | 14,298 |
1970 | 11 | 454 | 2,171 | 4,352 |
1971 | 8 | 213 | 954 | 1,580 |
1972 | 122 | 2,100 | 8,858 | 13,978 |
1973 | 5 | 18 | 70 | 123 |
1974 | 1 | 150 | 512 | 933 |
1975 | 21 | 490 | 1,533 | 2,290 |
1976 | 9 | 100 | 299 | 400 |
1977 | 0 | 10 | 28 | 42 |
1978 | 36 | 20 | 49 | 100 |
1979 | 22 | 3,045 | 6,769 | 11,264 |
1980 | 2 | 300 | 599 | 1,128 |
1981 | 0 | 25 | 46 | 102 |
1982 | 0 | Minor | Minor | 36 |
1983 | 22 | 2,000 | 3,523 | 5,289 |
1984 | 4 | 66 | 112 | 170 |
1985 | 30 | 4,000 | 6,641 | 8,567 |
1986 | 9 | 17 | 27 | 38 |
1987 | 0 | 8 | 12 | 17 |
1988 | 6 | 59 | 88 | 115 |
1989 | 56 | 7,670 | 10,989 | 13,436 |
1990 | 13 | 57 | 79 | 96 |
1991 | 16 | 1,500 | 2,064 | 2,234 |
1992 | 24 | 26,500 | 35,993 | 43,152 |
1993 | 4 | 57 | 74 | 83 |
1994 | 38 | 973 | 1,222 | 1,339 |
1995 | 29 | 3,723 | 4,498 | 4,860 |
1996 | 36 | 3,600 | 4,251 | 4,544 |
1997 | 4 | 100 | 114 | 121 |
1998 | 23 | 4,344 | 5,990 | 5,484 |
1999 | 62 | 5,532 | 5,907 | 6,222 |
2000 | 6 | 27 | 28 | 32 |
2001 | 45 | 5,260 | 6,314 | 6,254 |
2002 | 9 | 1,220 | 1,424 | 1,411 |
2003 | 24 | 3,600 | 4,007 | 3,970 |
2004 | 60 | 45,000 | 46,337 | 45,000 |
2005 | 2,067 | 120,000 | 120,000 | 120,000 |
2006 | 0 | 500 | 484 | — |
2007 | 10 | 50 | 48 | — |
2008 | 41 | 25,370 | 23,013 | — |
2009 | 6 | 0 | 0 | 0 |
2010 | 11 | 258 | 231 | — |
2011 | 52 | 15,800 | 13,720 | — |
2012 | 86 | 73,550 | 62,564 | — |
2013 | 1 | Minor | Minor | — |
2014 | 0 | 2 | 1.6 | — |
2015 | 10 | 17.9 | 14.8 | — |
2016 | 24 | 10,550 | 8,584 | — |
2017 | 203 | 140,360 | 111,832 | — |
2018 | 59 | 49,375 | 38,401 | — |
2019 | 17 | 7,200 | 5,500 | — |
Adjusted – Adjusted to 2005 dollars based on U.S. Department of Commerce Implicit Price Deflator for Construction.
Normalized – Normalization reflects inflation changes in personal wealth and coastal county population to 2004. (Pielke and Landsea 1998)
1 1900 could have been as high as 12,000.
2 Considered too high in 1915 reference.
3 Using 1915 cost adjustment – none available
prior to 1915.
Hurricanes Vs. Tornadoes
Tornadoes
Tornadoes have diameters on the scale of 100s of meters and are produced from a single convective storm (i.e. a thunderstorm or cumulonimbus). The strongest tornadoes – those of Fujita Tornado Damage Scale 4 and 5 – have estimated winds of 207 mph [333 kph] and higher.
Tornadoes require substantial
vertical shear of the horizontal winds (i.e. change of wind speed and/or direction with height) to provide ideal conditions for tornado genesis.
Tornadoes are primarily an over-land phenomena as solar heating of the land surface usually contributes toward the development of the thunderstorm that spawns the vortex (though over-water tornadoes have occurred).
Tornadoes typically last on the scale of minutes. The roughly 1000 tornadoes that impact the continental U.S. each year cause about
ten times less – about $500 million in total.
Tornadoes, in contrast, tend to be a mile or smaller in diameter, last for minutes and primarily cause damage from their extreme winds.
Hurricanes or Tropical Cyclones
A tropical cyclone has a diameter on the scale of 100s of *kilometers* and is comprised of several to dozens of convective storms. The strongest hurricanes – those of Saffir-Simpson Hurricane Scale 4 and 5 – have winds of 131 mph [210 kph] and higher.
Tropical cyclones require very low values (less than 10 m/s [20 kt, 23 mph]) of tropospheric vertical shear in order to form and grow. Tropical cyclones are purely an oceanic phenomenon – they die out over-land due to a loss of a moisture source, and have a lifetime that is measured in days
Hurricanes tend to cause much more destruction than tornadoes because of their size, duration and variety of ways to damage items. The destructive circular eyewall in hurricanes (that surrounds the calm
eye) can be tens of miles across, last hours and damage structures through storm surge, rainfall-caused flooding, as well as wind impacts. Hurricanes in the continental U.S. cause on average about $3 billion per landfall and about $5 billion annually.
References:
Brooks, H. E., and C. A. Doswell, III, 2001: Normalized damage from major tornadoes in the United States: 1890-1999. Wea. Forecasting , 16, 168-176.
Jarrell,J.D., M. Mayfield, E.N. Rappaport, and C.W.
Landsea, 2001: “The Deadliest, Costliest, and Most Intense United States Hurricanes from 1900 to 2000 (and other Frequently Requested Hurricane Facts)”NOAA Technical Memorandum NWS/TPC-1
Why Do Tropical Cyclones Spawn Tornadoes and How Often Does it Happen?
Tropical cyclones spawn tornadoes when certain instability and vertical shear criteria are met, in a manner similar to other tornado-producing systems. However, in tropical cyclones, the vertical structure of the atmosphere differs somewhat from that most often seen in midlatitude systems. In particular, most of the thermal instability is found near or below 10,000 feet altitude, in contrast to midlatitude systems, where the instability maximizes typically above 20,000 feet. Because the instability in TC’s is focussed at low altitudes, the storm cells tend to be smaller and shallower than those usually found in most severe mid latitude systems. But because the vertical shear in TC’s is also very strong at low altitudes, the combination of instability and shear can become favorable for the production of small supercell storms, which have an enhanced likelihood of spawning tornadoes compared to ordinary thunderstorm cells (Novlan and Gray 1974, Gentry 1983, McCaul 1991).
Almost all tropical cyclones making landfall in the United States spawn at least one tornado, provided enough of the TC’s circulation moves over land. This implies that Gulf coast landfalling TC’s are more likely to produce tornadoes than Atlantic coast TC’s that “sideswipe” the coastline. The rate at which TC’s produce tornadoes (waterspouts) over the ocean is unknown, although Doppler radars have identified many cases where storm cell rotation suggestive of the presence of tornadoes was observed over water, and there have been a number of cases where TC-spawned waterspouts have been witnessed from shore, with some of these coming ashore as tornadoes (McCaul, 1991).
What Parts of a Tropical Cyclone Are Most Favored for Tornado Formation?
In the northern hemisphere, the right-front quadrant (relative to TC motion) of recurving TCs is strongly favored. In the southern hemisphere, the left-front quadrant presumably is favored, although there is little research on this point. Most of the tornadoes form in outer rainbands some 50-300 miles from the TC center, but some have been documented to occur in the inner core, or even in the TC eyewall (Novlan and Gray, 1974; McCaul, 1991).
Why Are Tropical Cyclone-spawned Tornadoes Especially Difficult to Deal With?
TC tornadoes are often spawned by unusually small storm cells that may not appear particularly dangerous on weather radars, especially if the cells are located more than about 60 miles from the radar. In addition, these small storms often tend to produce little or no lightning or thunder, and may not look very threatening visually to the average person. Furthermore, the tornadoes are often obscured by rain, and the storm cells spawning them may move rapidly, leaving little time to take evasive action once the threat has been perceived. (McCaul et al. 1996, Spratt et al. 1997).
Which States Are Most Vulnerable to TC Tornadoes Outbreaks?
Historical records show that the largest and most intense TC tornado outbreaks have occurred in states bordering the Gulf coast and the Atlantic coast from Virginia southward. The biggest outbreaks have occurred (starting from west to east, not in order of outbreak size or severity) in Texas (from Carla in 1961, Beulah in 1967, Allen in 1980, Alicia in 1983, and Gilbert in 1988), Louisiana (Audrey in 1957, Carla in 1961, Hilda in 1964, Andrew in 1992, and Lili in 2002), Mississippi (Audrey in 1957, Andrew in 1992, and Rita in 2005), Alabama (Audrey in 1957, Danny in 1985, Georges in 1998, Cindy in 2005, and Rita in 2005), Georgia (Ivan in 2004, Cindy in 2005, Katrina in 2005), Florida (Agnes in 1972, Opal in 1995, Josephine in 1996, Charley in 2004, Frances in 2004, and Ivan in 2004), South Carolina (Beryl in 1994, Frances in 2004, Jeanne in 2004), North Carolina (Floyd in 1999, Frances in 2004), Virginia (Gracie in 1959, David in 1979, Frances in 2004, Gaston in 2004, and Ivan in 2004). The Gulf coast states tend to have the most frequent and significant TC tornado events, partly because of their tendency to have at least one state fully exposed to the right-front quadrant of the TC when landfall occurs there (McCaul 1991). However, the mid-Atlantic states can also get major outbreaks if the parent TC moves far enough inland during recurvature.
How Long After Landfall Are Tropical Cyclone-spawned Tornadoes a Threat?
Tropical cyclones spawn tornadoes when certain instability and vertical shear criteria are met, in a manner similar to other tornado-producing systems. However, in tropical cyclones, the vertical structure of the atmosphere differs somewhat from that most often seen in midlatitude systems. In particular, most of the thermal instability is found near or below 10,000 feet altitude, in contrast to midlatitude systems, where the instability maximizes typically above 20,000 feet. Because the instability in TC’s is focussed at low altitudes, the storm cells tend to be smaller and shallower than those usually found in most severe mid latitude systems. But because the vertical shear in TC’s is also very strong at low altitudes, the combination of instability and shear can become favorable for the production of small supercell storms, which have an enhanced likelihood of spawning tornadoes compared to ordinary thunderstorm cells (Novlan and Gray 1974, Gentry 1983, McCaul 1991).
Almost all tropical cyclones making landfall in the United States spawn at least one tornado, provided enough of the TC’s circulation moves over land. This implies that Gulf coast landfalling TC’s are more likely to produce tornadoes than Atlantic coast TC’s that “sideswipe” the coastline. The rate at which TC’s produce tornadoes (waterspouts) over the ocean is unknown, although Doppler radars have identified many cases where storm cell rotation suggestive of the presence of tornadoes was observed over water, and there have been a number of cases where TC-spawned waterspouts have been witnessed from shore, with some of these coming ashore as tornadoes (McCaul, 1991).
Are Tropical Cyclone Tornadoes Weaker than Mid Latitude Tornadoes?
TC’s may spawn tornadoes up to about three days after landfall. Statistics show that most of the tornadoes occur on the day of landfall, or the next day. However, many of the largest outbreaks have occurred two days after TC landfall, as the TC remnants interact with mid latitude weather systems. The most likely time for tornadoes is during daylight hours, although they can occur during the night too (McCaul, 1991).
What Is the Largest Known Outbreak of Tropical Cyclone-spawned Tornadoes?
2004’s Hurricane Ivan caused a multi-day outbreak of 127 tornadoes, with the bulk of the tornadoes on 17 September in the mid-Atlantic region, some two days after Ivan’s landfall in Alabama. State-by-state tornado counts from Ivan include Florida with 22, Georgia 25, Alabama 8, South Carolina 7, North Carolina 4, Virginia 40, West Virginia 3, Maryland 9, and Pennsylvania 9. There were 26
tornadoes on 15 September, 32 on 16 September, 63 on 17 September, 2 on 18 September, and 4 on 19 September. At least 7 people were killed and 17 injured by these tornadoes.
The previous record was during Hurricane Beulah, which spawned a reported 115 tornadoes in southeast Texas during the first several days after its landfall in September 1967 (Orton 1970). Frances of 2004 is close behind in third place, with 106 tornadoes, and Rita of 2005 is in fourth place with 92.
While it is difficult to predict which TCs will produce large tornado outbreaks, there is evidence suggesting that the likelihood of a major outbreak increases for TCs that are large, intense, are recurving and entering the westerlies, have forward speeds from about 8-18 mph, and are interacting with old, weakened frontal boundaries. In addition, the TC’s right-front quadrant must receive significant exposure to land, and this strongly favors TCs making landfall on the Gulf coast as opposed to those grazing the Carolinas (McCaul, 1991; McCaul et al., 2004).
What Was the Costliest Single Tropical Cyclone-spawned Tornado?
One of the tornadoes produced by Hurricane Allen in 1980 did about $50 million damage (1980 dollars; about $127 million damage in 2005 dollars) in the Austin, TX, area. More recently, Hurricane Cindy spawned a strong tornado that damaged the Atlanta Motor Speedway and other nearby areas to the tune of some $71.5 million in July 2005.
Useful Conversions
Winds
1
mile per hour = 0.869 international nautical mile per hour (knot)
1 mile per hour = 1.609 kilometers per hour
1 mile per hour = 0.4470 meter per second
1 knot = 1.852 kilometers per hour
1 knot = 0.5144 meter per second
1 meter per second = 3.6 kilometers per hour
Pressure
1 inch of mercury = 25.4 mm of mercury = 33.86 millibars = 33.86 hectoPascals
Distance
1 foot = 0.3048 meter
1 international nautical mile = 1.1508 statute miles = 1.852 kilometers = .99933 U.S nautical mile (obsolete)
1° latitude = 69.047 statute miles = 60 nautical miles = 111.12 kilometers
For longitude the conversion is
the same as latitude except the value is multiplied by the cosine of the latitude.
Legacy FAQ Index
Looking for the old FAQ? We are now sorting questions by topic. Here is an index below that will show you where your question is by the old sorting system. Please don’t hesitate to contact us at if you cannot find what you’re looking for.