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Hurricane Ivan

Hurricane Ivan

:This article deals with the 2004 Hurricane Ivan. For other storms of the same name, see Hurricane Ivan (disambiguation). Hurricane Ivan was the ninth named storm, the sixth hurricane, the fourth major hurricane, and the only category 5 hurricane of the 2004 Atlantic hurricane season. It formed on September 2 as a tropical depression, became a tropical storm on September 3, and a hurricane on September 5. It was a Cape Verde-type hurricane that reached Category 5 strength on the Saffir-Simpson Hurricane Scale, the highest possible category. Ivan also gained unprecedented intensity at low latitudes—Category 4 at only 10.6° N—after having existed for only a few days. Its minimum recorded pressure of 910 mbar makes it the ninth most intense Atlantic hurricane on record. It caused an estimated $13 billion worth of damage in the United States, making it the fourth costliest hurricane to ever strike the U.S. Ivan struck Grenada directly on mid-day September 7 at Category 3 intensity, causing at least 39 deaths and damage to over 85% of the structures on the island. It continued across the Caribbean Sea, reaching Category 5 intensity before passing close to the Jamaican coast and Grand Cayman and crossing the western tip of Cuba. Twenty deaths were reported in Jamaica, and damage to over 80% of the buildings was reported on Grand Cayman. Ivan then moved into the eastern Gulf of Mexico and weakened to a strong Category 3 storm. It continued on a track towards the north-northwest, making landfall in the U.S. near Gulf Shores, Alabama. After landfall, Ivan dropped heavy rains on the Southeastern United States, turned east, and then later looped south and through Florida and regenerated into a tropical storm for a short time in the Gulf of Mexico. The new tropical system moved into Louisiana and Texas, causing minimal damage. Ivan broke several hydrological records; it is credited with possibly causing the largest ocean wave ever recorded, a 91-foot (27 meter) wave that may have been as high as 131 feet (40 m), and the fastest seafloor current, at 2.25 meters per second (5 miles per hour). The name Ivan was retired in the spring of 2005 by the World Meteorological Organization and will be replaced by Igor in the 2010 season. World Meteorological Organization, 2004 from aboard the orbiting International Space Station (ISS) at an altitude of about 230 miles (370 km). Photo by science officer and flight engineer Edward Fincke.]]

Storm history

On September 2, 2004, Tropical Depression Nine formed about 555 miles (890 km) southwest of the Cape Verde Islands. The depression strengthened gradually to tropical storm status about 610 miles (980 km) southwest of the Cape Verde Islands, moving west-northwesterly at around 16 mph (25 km/h), and was given the name Ivan on September 3. Early September 5, Tropical Storm Ivan's winds strengthened to hurricane status 1210 miles (1950 km) east-southeast of the Lesser Antilles. By 5 PM EDT, Ivan had rapidly strengthened to a strong category three hurricane (nearly a category four) on the Saffir-Simpson Hurricane Scale with winds of 125 mph (200 km/h). The National Weather Service noted such rapid strengthening was unprecedented at such low latitudes in the Atlantic basin.

Caribbean

Atlantic at 19:45 UTC (15:45 EDT). At the time, Ivan had maximum sustained winds of 120 mph (195 km/h), placing it at Category 3 on the Saffir-Simpson Hurricane Scale. Visible satellite image courtesy NOAA.]] As Ivan traveled west, it weakened to a Category 2 hurricane. But on September 7, shortly after passing over Grenada on its way into the Caribbean Sea, it reattained Category 4 intensity with winds of 135 mph (215 km/h). Saint Lucia, St. Vincent, and Barbados were struck by the hurricane with Grenada suffering a significant direct battering for several hours. As Ivan was passing just north of the Windward Netherlands Antilles and Aruba on September 9, sustained wind speed increased to 160 mph (260 km/h) thus classifying Ivan as a Category 5 hurricane. Following this milestone, Ivan fluctuated between category 4 and 5 status, which is typical of intense hurricanes. Ivan continued west-northwest, heading straight for Jamaica. As Ivan approached the island late on September 10, it began a westward jog which kept the eye and the strongest winds to the south and west. However, because it still came very close to the Jamaican coast, and its winds were strongest on the north side, Jamaica still was battered with hurricane-force winds for hours. After clearing Jamaica, it resumed its more northerly track, and retained Category 5 intensity with sustained wind speeds of 165 mph (270 km/h). With minimum recorded central pressure at 910 millibars, Ivan is ranked as the ninth most intense Atlantic hurricane on record, as of 2005. Ivan spent most of September 11 traveling west at Category 4 strength, staying just off the southern coast of Jamaica. Ivan's intensity continued fluctuating, with the storm temporarily retaining Category 5 strength before passing within 30 miles (45 km) of Grand Cayman, bringing 180 mph winds onto the island. After passing the Cayman Islands, Ivan brushed the western tip of Cuba late on September 13, with its eyewall coming on shore. With most of its central circulation staying offshore, Ivan was able to pass through the Yucatan Channel with no loss of strength. Once over the Gulf of Mexico, Ivan lost some strength, dropping back to a 140 mph (225 km/h) Category 4 hurricane, but maintained that intensity as it traveled north to the coast of the United States.

United States

United States Around 2 AM CDT September 16 (0700 UTC), Ivan struck the U.S. mainland near Gulf Shores, Alabama. At the time, Ivan's maximum sustained winds had dropped to 130 mph (210 km/h), which placed it on the boundary of Category 3/4 (it was officially declared a Cat 3 at landfall, although some sources classified it as a Cat 4). This drop in strength was accompanied by a disruption of Ivan's eyewall. Both NEXRAD operators and Hurricane Hunters reported that the southwestern portion of the eyewall had all but disappeared in the hours before landfall. As Ivan approached landfall, Florida Lt. Governor Toni Jennings described it as "the size of Frances but [with] the impact of Charley". Ivan continued inland, maintaining hurricane strength until it was over central Alabama. The city of Demopolis, over 100 miles inland in west-central Alabama, endured wind gusts estimated at 90 mph, while Montgomery saw wind gusts in the 60–70 mph range at the height of the storm. [http://www.srh.noaa.gov/bmx/significant_events/Ivan] Late on the 16th, Ivan weakened to a tropical depression over northeastern Alabama. On September 18, remnants of Ivan drifted off the U.S. mid-Atlantic coast into the Atlantic Ocean, and the low pressure disturbance continued to dump rain on the east coast of the United States. Ivan lost tropical characteristics on September 18 while crossing Virginia. The remnant low crossed the coast of New Jersey later that day and advisories were discontinued. Nevertheless, on the morning of September 21, some of its remnants combined with a low-pressure system to pelt Cape Breton Island of Nova Scotia, Canada, with hurricane-force winds, flooding some roads, felling trees, and leaving thousands without power.

Ivan's "return"

Canada in the Gulf of Mexico after having traveled in a circular motion through the southeastern United States, causing tremendous flooding.]] An interesting development occurred on September 20 as a small surface low, caused by the southern remnants of Ivan, moved across the Florida peninsula. As it continued west across the northern Gulf of Mexico, the system organized and took on tropical characteristics. On September 22 the National Weather Service, "after considerable and sometimes animated in-house discussion [regarding] the demise of Ivan," determined that the low was in fact a result of the remnants of Ivan and thus named it accordingly. On the evening of September 23, the revived Ivan made landfall near Cameron, Louisiana, as a weak tropical storm. Ivan weakened quickly as it traveled overland into southeast Texas.

Preparations

In the Caribbean, 500,000 Jamaicans were told to evacuate from coastal areas, but only 5,000 were reported to have moved to shelters. 12,000 residents and tourists were evacuated from Isla Mujeres off Yucatan. In Louisiana, mandatory evacuations of vulnerable areas in Jefferson, Lafourche, Plaquemines, St. Charles, St. James, St. John the Baptist and Tangipahoa parishes took place, with voluntary evacuations in 6 other parishes ordered. More than one-third of the population of Greater New Orleans voluntarily evacuated. At the height of the evacuation, intense traffic congestion on local highways caused delays of up to 12 hours. About a thousand special-needs patients were housed at the Louisiana Superdome during the storm. In Mississippi, evacuation of mobile homes and vulnerable areas took place in Hancock, Jackson and Harrison counties. In Alabama, evacuation in the areas of Mobile and Baldwin counties south of Interstate 10 was ordered, including a third of the incorporated territory of the City of Mobile, as well as suburbs such as Daphne, Fairhope, Gulf Shores, Orange Beach, Robertsdale, Foley, Fort Morgan, Bayou La Batre, Dauphin Island, Point Clear, Belle Fontaine, Coden, Grand Bay, Mon Luis and Hollinger's Island. In Florida, a full evacuation of the Florida Keys began at 7:00 AM EDT September 10, but was lifted at 5:00 AM EDT September 13 as Ivan tracked further west than originally predicted. Voluntary evacuations were declared in ten counties along the Florida Panhandle, with strong emphasis in the immediate western counties of Escambia, Santa Rosa, and Okaloosa

Aftermath and recovery

Ivan killed 64 people in the Caribbean—mainly in Grenada and Jamaica—three in Venezuela, and 25 in the United States, including fourteen in Florida. Thirty-two more deaths in the United States were indirectly attributed to Ivan. Tornadoes spawned by Ivan struck communities along concentric arcs on the leading edge of the storm. Blountstown, Florida, Marianna, Florida and Panama City Beach suffered three of the most devastating tornadoes. A Panama City Beach news station was nearly hit by an F2 tornado during the storm. Ivan also caused over $13 billion in damages in the United States and $3 billion in the Caribbean.

Grenada

F2 Ivan passed directly over Grenada on September 7, 2004, killing 29 people. The capital, St. George's, was severely damaged and several notable buildings were destroyed, including the residence of the prime minister. Ivan also caused extensive damage to a local prison, allowing most of the inmates to escape. The island, in the words of a Caribbean disaster official, suffered "total devastation". According to a member of the Grenadan parliament, at least 85% of the small island was devastated. Extensive looting was reported. Grenada suffered serious economic repercussions following the destruction caused by Ivan. Before Ivan, the economy of Grenada was projected to grow by 4.7%, but the island's economy instead contracted by nearly 3% in 2004. The economy was also projected to grow by at least 5% through 2007, but, as of 2005, that estimate had been lowered to less than 1%. The government of Grenada also admitted that the government debt—130% of the island's GDP—was "unsustainable" in October 2004, and appointed a group of professional debt advisors in January 2005 to try to alleviate the situation. More than $150 million was sent to Grenada in 2004 to aid reconstruction following Ivan, but the economic situation remains fragile. The IMF reports that as "difficult enough as the present fiscal situation is, it is unfortunately quite easy to envisage circumstances that would make it even more so." Furthermore, "shortfalls in donor financing and tax revenues, or events such as a further rise in global oil prices, pose a grave risk."

Jamaica

On September 11–12, Ivan passed over Jamaica, causing significant wind and flood damage. Looters were reported roaming the streets of Jamaica's capital city, Kingston (which appeared deserted), robbing emergency workers at gunpoint. Overall, 18 people were killed in Jamaica and 18,000 people were left homeless as a result of the flood waters and high winds. Most of the major resorts and hotels fared well, though, and were reopened soon only a few days after Ivan had passed.

Cayman Islands

In the Cayman Islands, governor Bruce Dinwiddy described damage as "very, very severe and widespread." A quarter of buildings on the islands were reported to be uninhabitable, with 80% damaged to some extent. Much of Grand Cayman Island still remained without power, water or sewer services ten days later. After five months, barely half the pre-Ivan hotel rooms were usable.

Rest of the Caribbean

Elsewhere in the Caribbean, a pregnant woman was killed in Tobago when a tree fell on top of her home, while another casualty was caused to a 75-year-old Canadian woman that drowned in Barbados. There were also four deaths in the Dominican Republic, and four in Venezuela. Over one-hundred fifty homes on Barbados and around 60 homes in St. Vincent and the Grenadines were also reportedly damaged. The regions' Caribbean Development Bank estimates Ivan caused over $3 billion damage on island nations, mostly in the Cayman Islands, Grenada and Jamaica.

United States

Jamaica Along with the 14 deaths in Florida, Ivan is blamed for eight in North Carolina, two in Georgia, and one in Mississippi. There were an additional 32 deaths reported as indirectly caused by the storm. Ivan caused an estimated $13 billion in damage in the United States alone, making it the third costliest hurricane on record at the time, being very near Hurricane Charley's $14 billion but well below Hurricane Andrew's $26 billion. Hurricane Hugo, which had been the second costliest hurricane since 1992, dropped to fourth after Charley and Ivan. The heaviest damage as Ivan made landfall on the U.S. coastline was observed in Baldwin County in Alabama, where the storm's eye (and eyewall) made landfall, Pensacola, Pensacola Beach, dwellings situated far inland along the shorelines of Escambia Bay, East Bay, and Blackwater Bay in Escambia County and Santa Rosa County, and Fort Walton Beach, Florida on the eastern side of the storm. The area just west of Pensacola, including the community of Warrington which includes Pensacola NAS, Perdido Key, and Southwest Escambia County, took the brunt of the storm. Some of the subdivisons in this part of the county were completely destroyed. Shattered windows from gusts and flying projectiles experienced throughout the night of the storm were common. Early estimates had put damage in the United States at $5–$15 billion. Escambia County near Pensacola]] In Pensacola, the Interstate 10 bridge across Escambia Bay was heavily damaged, with as much as a quarter mile (400 m) of the bridge collapsing into the bay. The causeway that carries U.S. Highway 90 across the northern part of the same bay was also heavily damaged. Virtually all of Perdido Key, an area on the outskirts of Pensacola that bore the brunt of Ivan's winds and rain, was essentially leveled. High surf and wind brought extensive damage to Innerarity Point as well as Orange Beach just over the border from the Key in Alabama. Alabama Further inland, Ivan caused major flooding, bringing the Chattahoochee River near Atlanta and many other rivers and streams to levels at or near 100-year records. The Delaware River and its tributaries crested just below their all-time records set by Hurricane Diane in 1955. In Western North Carolina, many streams and rivers reached well above flood stage causing many roads to be closed. The Blue Ridge Parkway as well as Interstate 40 through the Pigeon River gorge in Haywood County, North Carolina, sustained major damage. The hurricane also spawned deadly tornadoes as far north as Maryland, and destroyed seven oil platforms in the Gulf of Mexico. Finally, after Ivan regenerated in the Gulf of Mexico, it caused further heavy rainfall up to 8 inches (20 cm) in areas of Louisiana and Texas. Hurricane Ivan is also suspected of bringing spores of soybean rust from Venezuela into the United States, the first ever occurrences of soybean rust found in North America. Since the Florida soybean crop had already been mostly harvested, economic damage was limited. Some of the most severe outbreaks in South America have been known to reduce soybean crop yields by half or more.

Reference

#[http://www.jamaicaobserver.com/news/html/20040907T220000-0500_65921_OBS_IVAN_AIMS_AT_JAMAICA.asp Ivan aims at Jamaica] - Wednesday, September 08, 2004 - Jamaica Observer

Footnotes

# #National Hurricane Center's [http://www.nhc.noaa.gov/archive/2004/dis/al092004.discus.067.shtml? Tropical Depression IVAN Special Discussion Number 67], September 22 2004 # # #[http://media.graytvinc.com/video/tornado.wmv Video of the tornado] # #Florida Department of Agriculture and Consumer Services (November 17, 2004). [http://www.doacs.state.fl.us/press/2004/11172004_2.html Soybean Rust Confirmed In Florida] # # # #

External links

- [http://www.nhc.noaa.gov/2004ivan.shtml? NHC Tropical Cyclone Report for Hurricane Ivan]
- [http://www.nhc.noaa.gov/archive/2004/IVAN.shtml? NHC advisory archives for Hurricane Ivan]
- [http://www.hpc.ncep.noaa.gov/tropical2004/IVAN/IVAN_archive.shtml Hydrometeorological Prediction Center advisory archive on Tropical Depression Ivan]
- State Emergency Management sites:
- [http://www.alabama.gov/hurricanewatch.php Alabama]
- [http://www.myflorida.com/myflorida/hurricane/public_advisories.html Florida]
- [http://www.lsp.org/emergency.html Louisiana]
- [http://www.msema.org/index.htm Mississippi]
- [http://www.dem.dcc.state.nc.us North Carolina]
- [http://www.txdps.state.tx.us/dem/ Texas]
- [http://www.nnvl.noaa.gov/hurseas2004/frances1515zC-040905-1kg12.jpg Image displaying both Hurricane Ivan and Frances] (Very large file—about 2 MB. Please view the [http://www.nnvl.noaa.gov/cgi-bin/index.cgi?page=items&ser=108162&large=1 smaller version] if you have a slow connection)
- [http://www.paradise-inn-carriacou.com/slideshows/ivan.php Hurricane Ivan pictures of damage on Grenada and Carriacou]
- [http://www.floridamemory.com/PhotographicCollection/photo_exhibits/hurricanes.cfm Historic Images of Florida Hurricanes (State Archives of Florida )] Ivan (2004) Ivan Ivan (2004) Ivan Ivan Ivan Ivan Ivan Category:Historic weather events in the United States Category:2004 meteorology ja:ハリケーン・アイバン

Hurricane Ivan (disambiguation)

The name Ivan was used for three tropical cyclones in the Atlantic Ocean.
- 1980's Hurricane Ivan: north-central Atlantic, did not approach land
- (not used in 1986 and 1992)
- 1998's Hurricane Ivan: central Atlantic, did not approach land
- 2004's Hurricane Ivan: A Cape Verde-type hurricane that formed September 3. Reached unprecedented strength at low latitudes and topped out at Category 5 as the 8th most intense Atlantic hurricane on record. Struck the Windward Islands, Jamaica, the Cayman Islands and Cuba. Made landfall in Alabama as a Category 3 hurricane on September 16. The name Ivan was retired after the 2004 season, and will be replaced by Igor in the 2010 season. The name Ivan was also used in the Western Pacific.
- 1997's Typhoon Ivan: Typhoon Ivan and Typhoon Joan became Super Typhoons at the same time. Typhoon Ivan (Narsing) hit Philippines. Ivan
- Ivan Ivan Ivan

Tropical cyclone

:Hurricane and Typhoon redirect here. For other uses, see Hurricane (disambiguation) and Typhoon (disambiguation). Typhoon (disambiguation) on March 26, 2004.]] In meteorology, a tropical cyclone (or tropical depression, tropical storm, typhoon, or hurricane, depending on strength and geographical context) is a type of low pressure system which generally forms in the tropics. While they can be highly destructive, tropical cyclones are an important part of the atmospheric circulation system, which moves heat from the equatorial region toward the higher latitudes.

Terms for tropical cyclones

equatorial region]] Depending on the region, different terms are used to describe tropical cyclones with maximum sustained winds exceeding 33 meters per second (63 knots, 73 mph, or 117 km/h):
- hurricane in the North Atlantic Ocean, North Pacific Ocean east of the dateline
- typhoon in the Northwest Pacific Ocean west of the dateline
- severe tropical cyclone in the Southwest Pacific Ocean west of 160°E or Southeast Indian Ocean east of 90°E
- severe cyclonic storm in the North Indian Ocean
- tropical cyclone in the Southwest Indian Ocean and South Pacific Ocean east of 160°E.
- cyclone unofficially in the South Atlantic Ocean In other areas, hurricanes have been called Baguio in the Philippines and Taino in Haiti.

Etymology

The word typhoon has two possible origins:
- From the Chinese 大風 (daaih fūng (Cantonese); dà fēng (Mandarin)) which means "great wind". (The Chinese term as 颱風 táifēng, and 台風 taifu in Japanese, has an independent origin traceable variously to 風颱, 風篩 or 風癡 hongthai, going back to Song 宋 (960-1278) and Yuan 元(1260-1341) dynasties. The first record of the character 颱 appeared in 1685's edition of Summary of Taiwan 臺灣記略).
- From Urdu, Persian or Arabic ţūfān (طوفان) < Greek tuphōn (Τυφών). Portuguese tufão is also related to typhoon. See tuphōn for more information. The word hurricane is derived from the name of a native Caribbean Amerindian storm god, Huracan, via Spanish huracán. The word cyclone came from the Greek word "κύκλος", meaning "circle".

Mechanics of a tropical cyclone

Spanish. The air heats up, rising further, which leads to more condensation. The air flowing out of the top of this “chimney” drops towards the ground, forming powerful winds.]] Structurally, a tropical cyclone is a large, rotating system of clouds, wind and thunderstorm activity. Its primary energy source is the release of the heat of condensation from water vapor condensing at high altitudes, the heat ultimately derived from the sun. Therefore, a tropical cyclone can be thought of as a giant vertical heat engine supported by mechanics driven by physical forces such as the orbital revolution and gravity of the Earth. Continued condensation leads to higher winds, continued evaporation, and continued condensation, feeding back into itself. This gives rise to factors that give the system enough energy to be self-sufficient and cause a positive feedback loop where it can draw more energy as long as the source of heat, warm water, remains. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The orbital revolution of the Earth causes the system to spin, giving it a cyclone characteristic and affecting the trajectory of the storm. The factors to form a tropical cyclone include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist and allow it to create a feedback loop by maximizing the energy intake possible, for example, such as high winds to increase the rate of evaporation, they can combine to produce the violent winds, incredible waves, torrential rains, and floods associated with this phenomenon. Condensation as a driving force is what primarily distinguishes tropical cyclones from other meteorological phenomena, and because this is strongest in a tropical climate, this defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclones, for example, draw their energy mostly from pre-existing horizontal temperature gradients in the atmosphere. In order to continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the atmospheric moisture needed. The condensation of this moisture is driven by the high winds and reduced atmospheric pressure in the storm, resulting in a sustaining cycle. As a result, when a tropical cyclone passes over land, its strength diminishes rapidly. Scientists at the National Center for Atmospheric Research estimate that a hurricane releases heat energy at the rate of 50 to 200 trillion watts -- about the amount of energy released by exploding a 10-megaton nuclear bomb every 20 minutes [http://www.ucar.edu/news/features/hurricanes/index.shtml].

Formation

nuclear bomb The formation of tropical cyclones is the topic of extensive ongoing research, and is still not fully understood. Five factors are necessary to make tropical cyclone formation possible: # Sea surface temperatures above 26.5 degrees Celsius (79.7 degrees Fahrenheit) to at least a depth of 50 meters (164 feet). The moisture in the air above the warm water is the energy source for tropical cyclones. # Upper-atmosphere conditions conducive to thunderstorm formation. Temperature in the atmosphere must decrease quickly with height, and the mid-troposphere must be relatively moist. # A pre-existing weather disturbance. This is most frequently provided by tropical waves—non-rotating areas of thunderstorms that move through tropical oceans. # A distance of approximately 10 degrees or more from the equator, so that the Coriolis effect is strong enough to initiate the cyclone's rotation. (2004's Hurricane Ivan was the strongest storm to form closer than 10 degrees from the equator; it started forming at 9.7 degrees north.) # Low vertical wind shear (change in wind speed or direction over height). High wind shear can break apart the vertical structure of a tropical cyclone. Tropical cyclones occasionally form despite not meeting these conditions. Only specific weather disturbances can result in tropical cyclones. These include: # Tropical waves, or easterly waves, which, as mentioned above, are westward moving areas of convergent winds. This often assists in the development of thunderstorms, which can develop into tropical cyclones. Most tropical cyclones form from these. A similar phenomenon to tropical waves are West African disturbance lines, which are squally lines of convection that form over Africa and move into the Atlantic. # Tropical upper tropospheric troughs, which are cold-core upper level lows. A warm-core tropical cyclone may result when one of these (on occasion) works down to the lower levels and produces deep convection. # Decaying frontal boundaries may occasionally stall over warm waters and produce lines of active convection. If a low level circulation forms under this convection, it may develop into a tropical cyclone.

When do tropical cyclones form?

Worldwide, tropical cyclone activity peaks in late summer when water temperatures are warmest. However, each particular basin has its own seasonal patterns. In the North Atlantic, a distinct hurricane season occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the North Atlantic hurricane season is September 10. The Northeast Pacific has a broader period of activity, but in a similar timeframe to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere, tropical cyclone activity begins in late October and ends in May. Southern Hemisphere activity peaks in mid-February to early March. Worldwide, an average of 80 tropical cyclones form each year.

Where do tropical cyclones form?

Most tropical cyclones form in a worldwide band of thunderstorm activity called the Intertropical convergence zone (ITCZ). Nearly all of them form between 10 and 30 degrees of the equator and 87% form within 20 degrees of it. Because the Coriolis effect initiates and maintains tropical cyclone rotation, such cyclones almost never form or move within about 10 degrees of the equator [http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/figures_ch1/figure1.9.htm], where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary if there is another source of initial rotation. These conditions are extremely rare, and such storms are believed to form at most once per century. Hurricane Ivan of 2004 developed within 10 degrees of the equator. A combination of a pre-existing disturbance, upper level divergence and a monsoon-related cold spell led to Typhoon Vamei at only 1.5 degrees north of the equator in 2001. It is estimated that such conditions occur only once every 400 years.

Major basins

There are seven main basins of tropical cyclone formation:
- North Atlantic Basin: The most-studied of all tropical basins, it includes the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. Tropical cyclone formation here varies widely from year to year, ranging from over twenty to one per year. The average is about ten. The United States Atlantic coast, Mexico, Central America, the Caribbean Islands and Bermuda are frequently affected by storms in this basin. Venezuela, the south-east of Canada and Atlantic "Macaronesian" islands are also occasionally affected. The U.S. National Hurricane Center (NHC) based in Miami, Florida, issues forecasts for storms for all nations in the region; the Canadian Hurricane Centre, based in Halifax, Nova Scotia, also issues forecasts and warnings for storms expected to affect Canadian territory and waters. Hurricanes that strike Mexico, Central America, and Caribbean island nations, often do intense damage, as hurricanes are deadlier over warmer water. Additionally, they can hit the coast of the U.S., especially Florida, North Carolina, the U.S. Gulf Coast and occasionally New Jersey, New York and New England (usually hurricanes weaken to tropical storms before they reach these northern regions). The coast of Atlantic Canada receives hurricane landfalls on rare occasion, such as Hurricane Juan in 2003. Many of the more intense Atlantic storms are Cape Verde-type hurricanes, which form off the west coast of Africa near the Cape Verde islands.
- Western North Pacific Ocean: Tropical storm activity in this region frequently affects China, Japan, the Philippines, and Taiwan, but also many other countries in South-East Asia, such as Vietnam, South Korea and Indonesia, plus numerous Oceanian islands. This is by far the most active basin, accounting for one-third of all tropical cyclone activity in the world. The eastern coasts of Taiwan and Philippines also have the highest tropical cyclone landfall frequency in the world. National meteorology organizations and the Joint Typhoon Warning Center (JTWC) are responsible for issuing forecasts and warnings in this basin.
- Eastern North Pacific Ocean: This is the second most active basin in the world, and the most dense (a large number of storms for a small area of ocean). Storms that form here can affect western Mexico, Hawaii, northern Central America, and on extremely rare occasions, California. In the U.S., the Central Pacific Hurricane Center is responsible for forecasting the western part of this area while the National Hurricane Center is responsible for the eastern part.
- South Western Pacific Ocean: Tropical activity in this region largely affects Australia and Oceania, and is forecast by Australia and Papua New Guinea.
- Northern Indian Ocean: This basin is divided into two areas, the Bay of Bengal and the Arabian Sea, with the Bay of Bengal dominating (5 to 6 times more activity). This basin's season has an interesting double peak; one in April and May before the onset of the monsoon, and another in October and November just after. Hurricanes which form in this basin have historically cost the most lives — most notably, the 1970 Bhola cyclone killed 200,000. Nations affected by this basin include India, Bangladesh, Sri Lanka, Thailand, Myanmar, and Pakistan, and all of these countries issue regional forecasts and warnings. Rarely, a tropical cyclone formed in this basin will affect the Arabian Peninsula.
- Southeastern Indian Ocean: Tropical activity in this region affects Australia and Indonesia, and is forecast by those nations.
- Southwestern Indian Ocean: This basin is the least understood, due to a lack of historical data. Cyclones forming here impact Madagascar, Mozambique, Mauritius, and Kenya, and these nations issue forecasts and warnings for the basin.

Unusual formation areas

Kenya at 2300 UTC near the Madeira Islands.]] The following areas spawn tropical cyclones only very rarely.
- Southern Atlantic Ocean: A combination of cooler waters, the lack of an ITCZ, and wind shear makes it very difficult for the Southern Atlantic to support tropical activity. However, three tropical cyclones have been observed here — a weak tropical storm in 1991 off the coast of Africa, Hurricane Catarina (sometimes also referred to as Aldonça), which made landfall in Brazil in 2004 as a Category 1 hurricane, and a smaller storm in January 2004, east of Salvador, Brazil. The January storm is thought to have reached tropical storm intensity based on scatterometre winds.
- Central North Pacific: Shear in this area of the Pacific Ocean severely limits tropical development. However, this region is commonly frequented by tropical cyclones that form in the much more favorable Eastern North Pacific Basin.
- Eastern South Pacific: Tropical cyclones are rare in this region; activity is frequently linked to El Niño episodes. When they do form, they can affect the islands of Polynesia.
- Mediterranean Sea: Storms which appear similar to tropical cyclones in structure sometimes occur in the Mediterranean basin. Such cyclones formed in September 1947, September 1969, January 1982, September 1983, and January 1995. However, there is debate on whether these storms were tropical in nature.
- Northeastern Atlantic Ocean: In October 2005, Hurricane Vince formed near Madeira, then moved northeastward, passing south of the Portuguese south coast, and made landfall in southwestern Spain as a tropical storm. Vince's origin was the northernmost in the eastern Atlantic ever recorded, and Vince was the first storm in recorded history to reach the Iberian Peninsula as a tropical cyclone, i.e. before being transformed into an extratropical low or absorbed into other systems of low pressure.
- Australia: SW Pacific Basin includes the eastern part of Australia and the Fiji area.
- Australia: SE Indian Basin includes the eastern part of the Indian ocean and the northern and western part of the Australian basin.
- Southern South China Sea Tropical cyclones normally do not develop in the Southern South China Sea due to its close proximity to the equator. Areas within ten degrees laditude of the equator do not experience a significant coriolis force, a vital ingredient in tropical cyclone formation. However, in December 2001, Typhoon Vamei formed in the Southern South China Sea and made landfall in Malaysia. It caused flooding in southern Malaysia and some damage in Singapore. It formed from a thunderstorm formation in Borneo that moved into the South China Sea.

Average Season

Structure and classification

Borneo A strong tropical cyclone consists of the following components.
- Surface low: All tropical cyclones rotate around an area of low atmospheric pressure near the Earth's surface. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level.
- Warm core: Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation as moist air is carried upwards and its water vapor condenses. This heat is distributed vertically, around the center of the storm. Thus, at any given altitude (except close to the surface where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.
- Central Dense Overcast (CDO): The Central Dense Overcast is a dense shield of very intense thunderstorm activity that make up the inner portion of the hurricane. This contains the eye wall, and the eye itself. The classic hurricane contains a symmetrical CDO, which means that it is perfectly circular and round on all sides.
- Eye: A strong tropical cyclone will harbor an area of sinking air at the center of circulation. Weather in the eye is normally calm and free of clouds (however, the sea may be extremely violent). Eyes are home to the coldest temperatures of the storm at the surface, and the warmest temperatures at the upper levels. The eye is normally circular in shape, and may range in size from 8 km to 200 km (5 miles to 125 miles) in diameter. In weaker cyclones, the CDO covers the circulation center, resulting in no visible eye.
- Eyewall: It is the area directly around the eye of the cyclone where the winds are the highest, the clouds reach furthest into the atmosphere and the precipitation is the heaviest. The heaviest damage caused by tropical cyclones occurs where the eyewall crosses over land.
- Outflow: The upper levels of a tropical cyclone feature winds headed away from the center of the storm with an anticyclonic rotation. Winds at the surface are strongly cyclonic, weaken with height, and eventually reverse themselves. Tropical cyclones owe this unique characteristic to the warm core at the center of the storm.

Types of tropical cyclones

Tropical cyclones are classified into three main groups: tropical depressions, tropical storms, and a third group whose name depends on the region. A tropical depression is an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of less than 17 metres per second (33 knots, 38 mph, or 62 km/h). It has no eye, and does not typically have the spiral shape of more powerful storms. It is already becoming a low-pressure system, however, hence the name "depression". A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 and 33 meters per second (34–63 knots, 39–73 mph, or 62–117 km/h). At this point, the distinctive cyclonic shape starts to develop, though an eye is usually not present. Government weather services assign first names to systems that reach this intensity (thus the term named storm). At hurricane intensity, a tropical cyclone tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of the circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the eyewall, an area about 10 to 50 miles (16 to 80 kilometers) wide in which the strongest thunderstorms and winds circulate around the storm's center. The circulation of clouds around a cyclone's center imparts a distinct spiral shape to the system. Bands or arms may extend over great distances as clouds are drawn toward the cyclone. The direction of the cyclonic circulation depends on the hemisphere; it is counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere. Maximum sustained winds in the strongest tropical cyclones have been measured at more than 85 m/s (165 knots, 190 mph, 305 km/h). Intense, mature hurricanes can sometimes exhibit an inward curving of the eyewall top that resembles a football stadium: this phenomenon is thus sometimes referred to as stadium effect. Eyewall replacement cycles naturally occur in intense tropical cyclones. When cyclones reach peak intensity they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 5 to 15 miles. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening (i.e. the maximum winds die off a bit and the central pressure goes up). Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger. While the most obvious motion of clouds is toward the center, tropical cyclones also develop an outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through a chimney effect of the storm engine. This outflow produces high, thin cirrus clouds that spiral away from the center. The high cirrus clouds may be the first signs of an approaching hurricane.

Categories and ranking

Hurricanes are ranked according to their maximum winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest maximum winds, a Category 5 hurricane has the highest. The rankings are not absolute in terms of effects. Lower-category storms can inflict greater damage than higher-category storms, depending on factors such as local terrain and total rainfall. In fact, tropical systems of less than hurricane strength can produce significant damage and human casualties, especially from flooding and landslides. The National Hurricane Center classifies hurricanes of Category 3 and above as Major Hurricanes. The Joint Typhoon Warning Center classifies typhoons with wind speeds of at least 150 mi/h (67 m/s or 241 km/h, equivalent to a strong Category 4 storm) as Super Typhoons. The definition of sustained winds recommended by the World Meteorological Organization (WMO) and used by most weather agencies is that of a 10-minute average. The U.S. weather service defines sustained winds based on 1-minute average speed measured about 10 meters (33 ft) above the surface.

Other storm systems

An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses. From space, extratropical storms have a characteristic "comma-shaped" cloud pattern. Extratropical cyclones can also be dangerous because their low-pressure centers cause powerful winds. In the United Kingdom and Europe, some severe northeast Atlantic cyclonic depressions are referred to as "hurricanes," even though they rarely originate in the tropics. These European windstorms can generate hurricane-force winds but are not given individual names. However, two powerful extratropical cyclones that ravaged France, Germany, and the United Kingdom in December 1999, "Lothar" and "Martin", were named due to their unexpected power (equivalent to a category 1 or 2 hurricane). In British Shipping Forecasts, winds of force 12 on the Beaufort scale are described as "hurricane force." There is also a polar counterpart to the tropical cyclone, called a polar low.

Movement and track

Large-scale winds

Although tropical cyclones are large systems generating enormous energy, their movements over the earth's surface are often compared to that of leaves carried along by a stream. That is, large-scale winds—the streams in the earth's atmosphere—are responsible for moving and steering tropical cyclones. The path of motion is referred to as a tropical cyclone's track. The major force affecting the track of tropical systems in all areas are winds circulating around high-pressure areas. Over the North Atlantic Ocean, tropical systems are steered generally westward by the east-to-west winds on the south side of the Bermuda High, a persistent high-pressure area over the North Atlantic. Also, in the area of the North Atlantic where hurricanes form, trade winds, which are prevailing westward-moving wind currents, steer tropical waves (precursors to tropical depressions and cyclones) westward from off the African coast toward the Caribbean and North America.

Coriolis effect

The earth's rotation also imparts an acceleration (termed the Coriolis Acceleration or Coriolis Effect). This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents (i.e. in the north, the northern part of the cyclone has winds to the west, and the Coriolis force pulls them slightly north. The southern part is pulled south, but since it is closer to the equator, the Coriolis force is a bit weaker there). Thus, tropical cyclones in the Northern Hemisphere, which commonly move west in the beginning, normally turn north (and are then usually blown east), and cyclones in the Southern Hemisphere are deflected south, if no strong pressure systems are counteracting the Coriolis Acceleration. The Coriolis acceleration also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds. (Much of that is due to the conservation of angular momentum - air is drawn in from an area much larger than the cyclone such that the tiny angular velocity of that air will be magnified greatly when the distance to the storm center shrinks.)

Interaction with high and low pressure systems

Finally, when a tropical cyclone moves into higher latitude, its general track around a high-pressure area can be deflected significantly by winds moving toward a low-pressure area. Such a track direction change is termed recurve. A hurricane moving from the Atlantic toward the Gulf of Mexico, for example, will recurve to the north and then northeast if it encounters winds blowing northeastward toward a low-pressure system passing over North America. Many tropical cyclones along the U.S. East Coast and in the Gulf of Mexico are eventually forced toward the northeast by low-pressure areas which move from west to east over North America.

Track forecasting

Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system. With their understanding of the forces that act on tropical cyclones, and a wealth of data from earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. High-speed computers and sophisticated simulation software allow forecasters to produce computer models that forecast tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. But while track forecasts have become more accurate than 20 years ago, scientists say they are less skillful at predicting the intensity of tropical cyclones. They attribute the lack of improvement in intensity forecasting to the complexity of tropical systems and an incomplete understanding of factors that affect their development.

Landfall

Officially, "landfall" is when a storm's center (the center of the eye, not its edge) reaches land. Naturally, storm conditions may be experienced on the coast and inland well before landfall. In fact, for a storm moving inland, the landfall area experiences half the storm before the actual landfall. For emergency preparedness, actions should be timed from when a certain wind speed will reach land, not from when landfall will occur.

Unusual landfall areas

The following areas rarely have a recorded landfall of a tropical cyclone: Europe: Because of the high latitudes, the European mainland have only a handful recorded landfalls made by hurricanes and or tropical storms. Notable examples are Hurricane Debbie of 1961 and Hurricane Vince of 2005. Azores: Like Europe, the Azores have a some recorded landfalls of hurricanes and tropical storms. Canary Islands: Until Tropical Storm Delta of 2005, the Canary Islands were rarely affected by any tropical storm or hurricanes. West African Coast: No recorded landfall of a tropical storm or hurricane although some come close but bypass the area. Cape Verde Islands: Some records of landfall made by a tropical storm or hurricane, most notably 1982's Tropical Storm Beryl that killed 115 people. Venezuela: Rarely a tropical storm or hurricane makes landfall in this country. Notable examples are 1993's Tropical Storm Bret and Hurricane Joan of 1988. California: Rarely a tropical storm or hurricane have ever affected California. Notable storms were a tropical storm in 1939 and a hurricane in 1858. New Zealand: On rare circumstances, a cyclone or two have made landfall in that country.

Dissipation

A tropical cyclone can cease to have tropical characteristics in several ways:
- It moves over land, thus depriving it of the warm water it needs to power itself, and quickly loses strength. Most strong storms become disorganized areas of low pressure within a day or two of landfall. There is, however, a chance they could regenerate if they manage to get back over open warm water. If a storm is over mountains for even a short time, it can rapidly lose strength. This is, however, the cause of many storm fatalities, as the dying storm unleashes torrential rainfall, and in mountainous areas, this can lead to deadly mudslides. The storm loses strength slower over flatter or marshy areas than over mountainous terrain which disrupts the surface circulation of the storm more.
- It remains in the same area of ocean for too long, sucking up all the warm water. Without warm surface water, the storm cannot survive.
- It experiences wind shear, causing the convection to lose direction and the heat engine to break down.
- It can be weak enough to be consumed by another area of low pressure, disrupting it and joining to become a large area of non-cyclonic thunderstorms. (Such, however, can re-strengthen the non-tropical system as a whole.)
- It enters colder waters. This does not necessarily mean the death of the storm, but the storm will lose its tropical characteristics. These storms are extratropical cyclones.
- An outer eye wall forms (typically around 50 miles from the center of the storm), choking off the convection toward the inner eye wall. Such weakening is generally temporary unless it meets other conditions above. Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane force) winds and drop several inches of rainfall. When a tropical cyclone reaches higher latitudes or passes over land, it may merge with weather fronts or develop into a frontal cyclone, also called extratropical cyclone. In the Atlantic ocean, such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane-force wind speeds when they reach Europe as a European windstorm.

Artificial dissipation

In the 1960s and 1970s, the United States government attempted to weaken hurricanes in its Project Stormfury by seeding selected storms with silver iodide. It was thought that the seeding would disrupt the storm's eyewall, causing it to collapse and thus reduce the winds. The winds of Hurricane Debbie dropped as much as 30 percent, but then regained their strength after each of two seeding forays. In an earlier episode, disaster struck when a hurricane east of Jacksonville, Florida, was seeded, promptly changed its course, and smashed into Savannah, Georgia. Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10 percent chance of making landfall within 48 hours. This placed severe restrictions on the project, and when the Navy pulled out in 1972, it all but killed any further attempts at hurricane seeding in the Atlantic. It was later discovered that eyewall disruption happens naturally as part of eyewall replacement cycles, and so the success of the program was impossible to gauge. Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing icebergs into the tropical oceans; covering the ocean in a substance that inhibits evaporation; or blasting the cyclone apart with nuclear weapons. These approaches all suffer from the same flaw: tropical cyclones are simply too large for any of them to be practical [http://www.aoml.noaa.gov/hrd/tcfaq/C5f.html]. However, it has been suggested by some that we can change the course of a storm during its early stages of formation, (detailed by an article, Controlling Hurricanes, Scientific American, 2005), such as using satellite to alter the environmental conditions or, more realistically, spreading degradable film of oil over the ocean, which prevent water vapour from fueling the storm.

Monitoring, observation and tracking

Intense tropical cyclones pose a particular observation challenge. As they are a dangerous oceanic phenomenon, weather stations are rarely available on the site of the storm itself. Surface level observations are generally available only if the storm is passing over an island or a coastal area, or it has overtaken an unfortunate ship. Even in these cases, real-time measurement taking is generally possible only in the periphery of the cyclone, where conditions are less catastrophic. It is however possible to take in-situ measurements, in real-time, by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by US government hurricane hunters [http://www.hurricanehunters.com/]. The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engine turboprop cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch GPS dropsondes inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted Aerosonde, a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare[http://www.sunherald.com/mld/sunherald/12699210.htm]. Tropical cyclones far from land are tracked by weather satellites using visible light and infrared bands. These satellite images are received regularly on half hour intervals. As the hurricane approaches land, the cyclone can also be imaged remotely by a nationwide system of Doppler radar. Land-based Doppler radars play a crucial role during landfall because they give forecasters the ability to see the storms location and intensity minute by minute. Recently, university researchers have begun to deploy mobile weather stations fortified to withstand hurricane-force winds. The two largest programs are the Florida Coastal Monitoring Program [http://www.ce.ufl.edu/~fcmp] and the Wind Engineering Mobile Instrumented Tower Experiment [http://www.atmo.ttu.edu/WEMITE/wemite.html]. During landfall, the NOAA Hurricane Research Division compares and quality controls reconnaissance aircraft data—which include flight-level, GPS sonde and stepped frequency microwave radiometer wind speed estimates—to wind speed data transmitted in real-time from weather stations erected near or at the coast. The National Hurricane Center uses these data to evaluate conditions at landfall and to verify its forecasts.

Naming of tropical cyclones

Storms reaching tropical storm strength (winds exceeding 17 metres per second, 38 mph, or 62 km/h) are given names, to assist in recording insurance claims, to assist in warning people of the coming storm, and to further indicate that these are important storms that should not be ignored. These names are taken from lists which vary from region to region and are drafted a few years ahead of time. The lists are decided upon, depending on the regions, either by committees of the World Meteorological Organization (called primarily to discuss many other issues), or by national weather services involved in the forecasting of the storms. Each year, the names of particularly destructive storms (if there were any) are "retired" and new names are chosen to take their place.

Naming schemes

The WMO's Regional Association IV Hurricane Committee selects the names for Atlantic Basin and central and eastern Pacific storms. In the Atlantic and Eastern North Pacific regions, feminine and masculine names are assigned alternately in alphabetic order during a given season. The "gender" of the season's first storm also alternates year to year: the first storm of an odd-numbered year gets feminine name, while the first storm of an even-numbered year gets a masculine name. Six lists of names are prepared in advance, and each list is used once every six years. Five letters — "Q," "U," "X," "Y" and "Z" — are omitted in the Atlantic; only "Q" and "U" are omitted in the Eastern Pacific, so the format accommodates 21 or 24 named storms in a hurricane season. Names of storms may be retired by request of affected countries if they have caused extensive damage. The affected countries then decide on a replacement name of the same gender (and if possible, the same ethnicity) as the name being retired. If there are more than 21 named storms in an Atlantic season or 24 named storms in an Eastern Pacific season, the rest are named as letters from the Greek alphabet: the 22nd storm is called "Alpha," the 23rd "Beta," and so on. This was first necessary during the 2005 season when the names Alpha, Beta, Gamma, Delta, and Epsilon were all used. There is no precedent for a storm named with a Greek Letter causing enough damage to justify retirement; how this situation would be handled is unknown. In the Central North Pacific region, the name lists are maintained by the Central Pacific Hurricane Center in Honolulu, Hawaii. Four lists of Hawaiian names are selected and used in sequential order without regard to year. In the Western North Pacific, name lists are maintained by the WMO Typhoon Committee. Five lists of names are used, with each of the 14 nations on the Typhoon Committee submitting two names to each list. Names are used in the order of the countries' English names, sequentially without regard to year. Japan Meteorological Agency uses a secondary naming system in Western North Pacific that numbers a typhoon on the order it formed, resetting on December 31 of every year. The Typhoon Songda in September 2004 is internally called the typhoon number 18 and is recorded as the typhoon 0418 with 04 taken from the year. The Australian Bureau of Meteorology maintains three lists of names, one for each of the Western, Northern and Eastern Australian regions. There are also Fiji region and Papua New Guinea region names. The Seychelles Meteorological Service maintains a list for the Southwest Indian Ocean.

History of tropical cyclone naming

For several hundred years after Europeans arrived in the West Indies, hurricanes there were named after the saint's day on which the storm struck. The practice of giving storms people's names was introduced by Clement Wragge, an Anglo-Australian meteorologist at the end of the 19th century. He used feminine names and the names of politicians who had offended him. During World War II, tropical cyclones were given feminine names, mainly for the convenience of the forecasters and in a somewhat ad hoc manner. For a few years afterwards, names from the Joint Army/Navy Phonetic Alphabet were used. The modern naming convention came about in response to the need for unambiguous radio communications with ships and aircraft. As transportation traffic increased and meteorological observations improved in number and quality, several typhoons, hurricanes or cyclones might have to be tracked at any given time. To help in their identification, beginning in 1953 the practice of systematically naming tropical storms and hurricanes was initiated by the United States National Hurricane Center, and is now maintained by the WMO. In keeping with the common English language practice of referring to inanimate objects such as boats, trains, etc., using the female pronoun "she," names used were exclusively feminine. The first storm of the year was assigned a name beginning with the letter "A", the second with the letter "B", etc. However, since tropical storms and hurricanes are primarily destructive, some considered this practice sexist. The National Weather Service responded to these concerns in 1979 with the introduction of masculine names to the nomenclature. It was also in 1979 that the practice of preparing a list of names before the season began. The names are usually of English, French or Spanish origin in the Atlantic basin, since these are the three predominant languages of the region where the storms typically form.

Renaming of tropical cyclones

In most cases, a tropical cyclone retains its name throughout its life. However, a tropical cyclone may be renamed in several occasions. 1. A tropical storm enters the southwestern Indian Ocean from the east In the south Indian Ocean, RSMC la Reunion names a tropical storm once it crosses 90°E from the east, even though it has been named. In this case, the Joint Typhoon Warning Center (JTWC) will put two names together with a hyphen. Examples: Oscar-Itseng(2004), Adeline-Juliet(2005) 2. A tropical storm crosses from the Atlantic into the Pacific, or vice versa, before 2001 It was the policy of National Hurricane Center (NHC) to rename a tropical storm which crossed from Atlantic into Pacific, or vice versa. Examples: Cesar-Douglas(1996), Joan-Miriam(1988) In 2001, when Iris moved across Central America, NHC mentioned that Iris would retain its name if it regenerated in the Pacific. However, the Pacific tropical depression developed from the remnants of Iris was called Fifteen-E instead. The depression later became tropical storm Manuel. NHC explained that the Iris had dissipated as a tropical cyclone prior to entering the eastern North Pacific basin, the new depression was properly named Fifteen-E, rather than Iris. In 2003, when Larry was about to move across Mexico, NHC attempted to provide greater clarity: :Should Larry remain a tropical cyclone during its passage over Mexico into the Pacific, it would retain its name. However, a new name would be given if the surface circulation dissipates and then regenerates in the Pacific. Up to now, there has been no tropical cyclone retaining its name during the passage from Atlantic to Pacific, or vice versa. 3. Uncertainties of the continuation When the remnants of a tropical cyclone redevelop, the redeveloping system will be treated as a new tropical cyclone if there are uncertainties of the continuation, even though the original system may contribute to the forming of the new system. Example: TD10/TD12 (eventually developed into Hurricane Katrina) (2005) 4. Human faults Sometimes, there may be human faults leading to the renaming of a tropical cyclone. Example: Ken-Lola(1989)

Effects

Ken-Lola. Katrina was the most costly tropical cyclone in United States history.]] A mature tropical cyclone can release heat at a rate upwards of 6x10¹⁴ watts [http://www.noaa.gov/questions/question_082900.html]. Tropical cyclones on the open sea cause large waves, heavy rain, and high winds, disrupting international shipping and sometimes sinking ships. However, the most devastating effects of a tropical cyclone occur when they cross coastlines, making landfall. A tropical cyclone moving over land can do direct damage in four ways.
- High winds - Hurricane strength winds can damage or destroy vehicles, buildings, bridges, etc. High winds also turn loose debris into flying projectiles, making the outdoor environment even more dangerous.
- Storm surge - Tropical cyclones cause an increase in sea level, which can flood coastal communities. This is the worst effect, as cyclones claim 80% of their victims when they first strike shore.
- Heavy rain - The thunderstorm activity in a tropical cyclone causes intense rainfall. Rivers and streams flood, roads become impassable, and landslides can occur.
- Tornado activity - The broad rotation of a hurricane often spawns tornadoes. While these tornadoes are normally not as strong as their non-tropical counterparts, they can still cause tremendous damage. Tornado Often, the secondary effects of a tropical cyclone are equally damaging. They include:
- Disease - The wet environment in the aftermath of a tropical cyclone, combined with the destruction of sanitation facilities and a warm tropical climate, can induce epidemics of disease which claim lives long after the storm passes. One of the most common post-hurricane injuries is stepping on a nail in storm debris, leading to a risk of tetanus or other infection. Infections of cuts and bruises can be greatly amplified by wading in sewage-polluted water.
- Power outages - Tropical cyclones often knock out power to tens or hundreds of thousands of people (or occasionally millions if a large urban area is affected), prohibiting vital communication and hampering rescue efforts.
- Transportation difficulties - Tropical cyclones often destroy key bridges, overpasses, and roads, complicating efforts to transport food, clean water, and medicine to the areas that need it.

Beneficial effects of tropical cyclones

Although cyclones take an enormous toll in lives and personal property, they may bring much-needed precipitation to otherwise dry regions. Hurricane Camille averted drought conditions and ended water deficits along much of its path. Hurricane Floyd did the same thing in New Jersey in 1999. The destruction caused by Camille on the Gulf coast spurred redevelopment as well, greatly increasing local property values. On the other hand, disaster response officials point out that redevelopment encourages more people to live in clearly dangerous areas subject to future deadly storms (as shown by the effects of Hurricane Katrina). Of course, many former residents and businesses do relocate to inland areas away from the threat of future hurricanes as well. Hurricanes also help to maintain global heat balance by moving warm, moist tropical air to the mid-latitudes and polar regions.

Long term trends in cyclone activity

While the number of storms in the Atlantic has increased since 1995, there seems to be no signs of a global trend; the global number of tropical cyclones remains about 90 ± 10. [http://wind.mit.edu/~emanuel/anthro2.htm]. Atlantic storms are certainly becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. This can to a large extent be attributed to the number of people living in susceptible coastal area, and massive development in the region since the last surge in Atlantic hurricane activity in the 1960s. Often in part because of the threat of hurricanes, many coastal regions

Category 5

Category 5 can refer to either:
- Category 5 cable used for carrying data
- Category 5 computer virus as classified by Symantec Corporation for the most severe threat level.
- Category 5 hurricanes on the Saffir-Simpson Hurricane Scale.

2004 Atlantic hurricane season

The 2004 Atlantic hurricane season officially began on June 1, 2004, and lasted until November 30, 2004. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic Ocean. However, the 2004 season exceeded these conventional limits slightly, as Tropical Storm Otto formed on the last day of the season and lasted two days into December. The season was notable as one of the deadliest and costliest Atlantic hurricane seasons on record, with at least 3,132 deaths and roughly $42 billion (USD) in damage. The most notable storms for the season were Hurricanes Charley, Frances, Ivan, and Jeanne. Jeanne wreaked havoc in Haiti, killing approximately 3,000 people, while Ivan raged through Grenada, Jamaica, and the Cayman Islands before striking the U.S. Gulf Coast. Frances and Jeanne both hit the Bahamas at full force. Furthermore, all four of these hurricanes (plus one tropical storm) hit Florida, with Frances and Jeanne hitting nearly the exact same location within three weeks of each other. Flood waters in the southeastern United States were brought to near-record levels.

Season summary

The 2004 season had numerous unusual occurrences. The first named storm of the season formed on August 1, giving the season the fifth-latest start since 1952. Tropical Storm Bonnie and Hurricane Charley became the first storms to hit the same U.S. state (Florida) in a 24-hour period since 1906. For the remainder of the season, Florida was hit by three more hurricanes, Frances, Ivan, and Jeanne. This is the first time four hurricanes have hit one state in one season since four hurricanes hit the Texas coast in 1886, including the hurricane that destroyed the city of Indianola. Other storms were individually unusual. Hurricane Alex was the strongest hurricane on record to intensify north of 38 degrees latitude. One storm, Tropical Storm Earl, died out, and its remains crossed over into the Pacific Ocean, regenerated, and became Hurricane Frank in the eastern Pacific. Pacific Ocean August 2004 was unusually active, with eight named storms forming during the month. In an average year, only three or four storms would be named in August. The formation of eight named storms in August breaks the old record of seven for the month, set in the 1933 and 1995 seasons. It also ties with September in the 2002 season for the most Atlantic tropical storms to form in any month. 2002 season] The most unusual storm of the season was Hurricane Ivan. Ivan first impressed meteorologists by becoming the first major hurricane (category three or above) on record to form as low as 10 degrees latitude. Ivan was also recorded as the sixth most intense hurricane on record, with a minimum central pressure of 910 millibars. One very unusual occurrence in relation to Ivan happened on September 22, when a remnant low from Ivan—which had traveled in a circular motion over the southeastern United States—was reclassified as a tropical depression as it moved over the Gulf of Mexico. The system was given the name Ivan and eventually strengthened into a respectable tropical storm with winds of 65 mph before making landfall along the coast of Texas, causing minimal flooding and damage. The 2004 season was very deadly, with over 3,000 deaths related to the flooding rains or winds caused by the storms. Nearly all of the deaths were reported in Haiti following the floods and mudslides caused by then-Tropical Storm Jeanne. This season had 16 tropical depressions, 15 named storms, 9 hurricanes, and 6 major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Scale). The Accumulated Cyclone Energy figure of 225 ranks this as the third most active season since 1950 (behind the 1950 season itself and the 1995 season). Although not part of the traditional Atlantic hurricane season, one event in the South Atlantic was so unusual as to merit mention. On March 25, a tropical cyclone (unofficially named Cyclone Catarina) formed in the South Atlantic. Although its status is questioned, Catarina is considered to be the first hurricane to have formed in the South Atlantic since satellite observations began. It made landfall late on March 27 in the Brazilian state of Santa Catarina. The storm killed at least three and caused over $350 million in damage. The end of the season brought questions about the way the National Hurricane Center projects storm paths. In 2004, they started projecting storms five days out instead of three; this caused people in the five-day path to board up or evacuate from the storm, when in some cases it veered away from those areas. Three days is considered enough time to prepare for a storm, so some suggested five days created unneeded panic. However, the NHC decided to use the same maps for 2005.

Preseason forecasts

On May 17, prior to the start of the season, NOAA forecasters predicted a 50% probability of activity above the normal range, with 12–15 tropical storms, 6–8 of those becoming hurricanes, and 2–4 of those hurricanes reaching at least Category 3 strength on the Saffir-Simpson Hurricane Scale.[http://www.noaanews.noaa.gov/stories2004/s2225.htm] Noted hurricane expert Dr. William Gray's May 28 prediction was similar, with 14 named storms, 8 reaching hurricane strength, and 3 reaching Category 3 strength.[http://hurricane.atmos.colostate.edu/Forecasts/2004/june2004/] On August 6, Dr. Gray announced he had revised his predictions slightly downwards, citing warmer oceans, to 13 named storms, 7 hurricanes, and 3 reaching category 3. Several days later, NOAA released an updated prediction as well, with a 45% probability of above-normal activity, but the same number of storms forecast.[http://www.hurricaneprotectionmag.com/mag/winter2005/season-review.html] A normal season, as defined by NOAA, has 6 to 14 tropical storms, 4 to 8 of which reach hurricane strength, and 1 to 3 of those reaching Category 3 strength.[http://www.cpc.ncep.noaa.gov/products/outlooks/hurricane2002/hurricane2002_background.html] The season ended up with 16 tropical depressions, 15 named storms, 9 hurricanes, and six major hurricanes, placing it well above all forecasts.

Storms

Hurricane Alex

August 6 on August 3.]] The first storm of the season formed at the end of July off the coast of South Carolina, an unusually late start. Alex strengthened into a Category Two hurricane, and on August 3 came within ten miles (16 km) of the Outer Banks of North Carolina without making landfall. Damage was limited to flooding and wind damage, and in Dare County, North Carolina, was estimated at $2.4 million. One minor injury was reported. Alex later headed out to sea and strengthened to a 120-mile-per-hour (195 km/h) Category Three hurricane, making Alex only the second hurricane on record to have reached Category Three strength north of 38° N latitude. Alex became extratropical over the north Atlantic, where it continued to produce gale-force winds. For the official forecasts, see the NHC's [http://www.nhc.noaa.gov/archive/2004/ALEX.shtml? archive on Hurricane Alex] and their [http://www.nhc.noaa.gov/2004alex.shtml? Tropical Cyclone Report].

Tropical Storm Bonnie

On August 3, a tropical wave approaching the Lesser Antilles organized into a tropical depression, dubbed Tropical Depression Two, or TD2. As the storm traveled west over the islands, it dissipated on August 4. The remnants of Tropical Depression Two continued westward and, on August 9, had strengthened into Tropical Storm Bonnie 410 miles (660 km) south of the mouth of the Mississippi River. Although appearing disorganized, Bonnie showed unusual structure, with a closed eye wall and a ten-mile (16 km) eye being reported by hurricane hunters on the night of August 9 and morning of August 10. As a NHC forecaster described it, they are "almost unheard of in a system of this intensity." Bonnie was a very small storm, with tropical storm-force winds extending only 30 miles (50 km) out from the center. Bonnie made landfall as a weakening tropical storm just south of Apalachicola, Florida, around 11 a.m. CDT on August 12. Rain was fleeting with the landfall of the tropical system, as the Apalachicola area only experienced thunderstorms for a couple of hours. As Bonnie weakened to a tropical depression, it interacted with an approaching cold front, producing large amounts of rain along the East Coast. Bonnie then exited back into the Atlantic. At 11 p.m. August 13, what was left of Bonnie had lost tropical characteristics and was positioned beyond the New England seaboard. Bonnie did cause significant rainfall to coastal North Carolina and the New England states. Three deaths in Pender County, North Carolina were attributed to a tornado spawned by Bonnie. For the official forecasts, see:
- the NHC's [http://www.nhc.noaa.gov/archive/2004/BONNIE.shtml? archive on Tropical Storm Bonnie].
- the HPC's [http://www.hpc.ncep.noaa.gov/tropical2004/BONNIE/BONNIE_archive.shtml advisory archive on Bonnie after landfall]. See also the NHC's [http://www.nhc.noaa.gov/2004bonnie.shtml? Tropical Cyclone Report].

Hurricane Charley

tornado Hurricane Charley formed east of the Windward Islands on August 9 and moved rapidly west across the Caribbean. As it neared Jamaica, it became a hurricane and grazed that island on the August 11, passing through the Cayman Islands the next morning. On August 12 Charley passed over mainland Cuba as a Category 3 hurricane just west of Havana. On August 13, Charley unexpectedly underwent rapid strengthening, jumping from a Category 2 to a powerful Category 4 storm in a few hours, while at the same time taking a sharp turn to the northeast. Charley made landfall as a Category 4 hurricane near Port Charlotte, Florida. Although the storm caused serious damage, much of this was limited to a narrow swath associated with the hurricane's eye wall. Charley was a very fast-moving, compact storm, and so much of its damage was attributed to high winds rather than heavy rain, as is the case in most hurricanes. Charley remained a hurricane across the entire Florida peninsula and passed near Orlando and Daytona Beach. It later made a second landfall near North Myrtle Beach, South Carolina, on August 14. Charley dissipated near Cape Cod, Massachusetts on August 15. Charley caused approximately $14 billion in damage to the United States, making it the third costliest hurricane in U.S. history. Fifteen deaths were directly attributed to Charley; four in Jamaica, one in Cuba, and ten in Florida. For the official forecasts, see the NHC's [http://www.nhc.noaa.gov/archive/2004/CHARLEY.shtml? archive on Hurricane Charley] and their [http://www.nhc.noaa.gov/2004charley.shtml? Tropical Cyclone Report].

Hurricane Danielle

At 11 a.m. AST on August 13, a tropical wave formed into Tropical Depression Four around 275 miles (440 km) southeast of Cape Verde. It was the first of five Cape Verde-type hurricanes of 2004. Twelve hours later, TD4 strengthened and was named Tropical Storm Danielle. Late on August 14, Danielle's wind speeds increased, and it was classified as a hurricane. Danielle moved northwest, peaking at Category Two. It was predicted to curve towards the Azores, but on August 18 lost motion and slackened to a tropical storm. By August 19, the storm had become stationary with minimal storm strength 810 miles (1305 km) southwest of the Azores. The storm was downgraded to a tropical depression the next day, and degenerated to a broad low-pressure area on August 21. For the official forecasts, see the NHC's [http://www.nhc.noaa.gov/archive/2004/DANIELLE.shtml? archive on Hurricane Danielle] and their [http://www.nhc.noaa.gov/2004danielle.shtml? Tropical Cyclone Report].

Tropical Storm Earl

Earl formed initially as the fifth tropical depression of the season on August 13 east of the Lesser Antilles. After traveling west, it reached tropical storm strength on August 14 around 375 miles (605 km) southeast of Barbados. On August 15, Earl passed just south of Grenada and entered the Caribbean. The storm had degenerated by that point, and that night would have been classified as a tropical wave. However, the government of Venezuela denied access to their airspace for storm reconnaissance aircraft. An on-site assessment of Earl's circulation was needed, since satellite observations are inaccurate for that purpose. Earl also posed a threat to land, so advisories continued for another 12 hours. The next morning a reconnaissance aircraft was able to reach the storm. It found no closed circulation, and Earl was reclassified as a tropical wave at 11 a.m. AST on August 16. Remnants of the storm continued across the Caribbean and into Central America, later becoming Tropical Depression 8E and then Hurricane Frank in the Pacific Ocean (the first time since 1996, when Hurricane Cesar became Douglas in the Pacific). Earl caused minor damage to Grenada and St. Vincent and the Grenadines. For the official forecasts, see the NHC's [http://www.nhc.noaa.gov/archive/2004/EARL.shtml? archive on Tropical Storm Earl] and their [http://www.nhc.noaa.gov/2004earl.shtml? Tropical Cyclone Report.] See also 2004 Pacific hurricane season for information on Earl after it crossed oceans.

Hurricane Frances

2004 Pacific hurricane season] Frances began as Tropical Depression Six on August 24, and it became a named storm on August 25 while well east of the Windward Islands. Frances strengthened rapidly, reaching Category 4 intensity by August 27. Initially forecast to turn north and potentially threaten Bermuda, conditions changed and Frances's predicted track shifted westward. After grazing the Turks and Caicos Islands, it plowed through the Bahamas. From September 2 through September 4, Frances slowly grinded its way across the Bahamas. Its slow movement allowed a record 2.5 to 3 million Floridians to evacuate their homes. However, as it grinded its way across the Bahamas, it weakened to a Category 2 hurricane, although it was still a very large storm. After sitting stationary off the coast of Florida for nearly 24 hours, Frances finally moved onto the coast of Florida in the early hours of September 5. It traveled northwest over land, briefly emerging over the Gulf of Mexico and striking the Florida panhandle. As it passed over Georgia on September 6, it caused heavy rainfall across the southern U.S. Over 15 inches of rain were recorded in some places in North Carolina and Virginia, causing heavy flooding. Frances was downgraded to a tropical depression and dissipated over Pennsylvania on September 9. Damage to the United States was approximately $9 billion, making it the sixth costliest hurricane in U.S. history. Most of Hurricane Frances's damage occurred in Florida as a result of the storm's slow movement, large size, and long duration of winds. The storm is directly responsible for seven deaths; one in the Bahamas and six in the United States. Hurricane Frances also produced a record-setting 123 tornadoes as it moved its way through the United States. For official forecasts, see:
- the NHC's [http://www.nhc.noaa.gov/archive/2004/FRANCES.shtml? archive for Hurricane Frances].
- the HPC's [http://www.hpc.ncep.noaa.gov/tropical2004/FRANCES/FRANCES_archive.shtml advisory archive on Frances after landfall]. See also the NHC's [http://www.nhc.noaa.gov/2004frances.shtml? Tropical Cyclone Report.]

Hurricane Gaston

Tropical Depression Seven formed at 5 p.m. EDT (2100 UTC) on August 27, around 140 miles (225 km) southeast of Charleston, South Carolina. The depression meandered off the coast for the rest of the day, strengthening into Tropical Storm Gaston by midday August 28. At 10 a.m. EDT (1400 UTC) on August 29, Gaston made landfall on the coast of Bulls Bay, South Carolina, near the towns of McClellanville and Awendaw. It was downgraded to a tropical depression later that day. The storm made landfall in almost the same location as Hurricane Hugo in 1989. At landfall the storm was originally classified as just shy of hurricane strength. While wind damage in South Carolina was minimal, the slow-moving storm produced five to ten inches (125 to 250 mm) of rain along its path, causing extensive flooding. Gaston moved north over land, weakening to a tropical depression but still bringing torrential rain to central Virginia, where at least eight people were killed in the ensuing floods. The Shockoe Bottom entertainment district near downtown Richmond, Virginia was devastated by the flooding. Total damage was estimated at about $130 million. Late on August 30, as Tropical Depression Gaston crossed Chesapeake Bay, its winds strengthened, and it was again classified as a tropical storm. It headed out over the Atlantic and became extratropical on September 1, about 185 miles (300 km) southeast of Halifax, Nova Scotia. On November 19, after a detailed analysis by the NHC, surface-level winds were determined to be about 75 mph (120 km/h) at landfall, and Gaston was reclassified as a Category 1 hurricane. For official forecasts, see the NHC's [http://www.nhc.noaa.gov/archive/2004/GASTON.shtml? archive on Hurricane Gaston] and their [http://www.nhc.noaa.gov/2004gaston.shtml? Tropical Cyclone Report.]

Tropical Storm Hermine

Hermine formed out of an organized area of disturbed weather that had formed about 325 miles (520 km) southeast of Cape Hatteras, North Carolina, or 360 miles (580 km) west of Bermuda and moved very rapidly north towards Cape Cod. On its northward trek, Hermine left behind most of its convection. The storm made landfall near New Bedford, Massachusetts, early on August 31, appearing as little more than a low-level swirl of clouds. It became extratropical a few hours later. Some rainfall and thunderstorms over Long Island and parts of New England were attributed to Hermine, but most people did not realize a tropical storm had struck. There were no casualties or reports of damage caused by Hermine. For the official forecasts, see the NHC's [http://www.nhc.noaa.gov/archive/2004/HERMINE.shtml? archive on Tropical Storm Hermine] and their [http://www.nhc.noaa.gov/2004hermine.shtml? Tropi