Traditionally, areas oftropical cyclone formation are divided into seven basins. These include the NorthAtlantic Ocean, the eastern and western parts of the NorthPacific Ocean, the Southwest Pacific, the Southwest and SoutheastIndian Oceans, and the North Indian Ocean (Arabian Sea andBay of Bengal). The West Pacific is the most active and the north Indian the least active. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones, super typhoons, or major hurricanes (at least ofCategory 3 intensity).^[1]

This region includes the NorthAtlantic Ocean, theCaribbean Sea, and theGulf of Mexico. Tropical cyclone formation here varies widely from year to year, ranging from one to over twenty-five per year.^[6] Most Atlantictropical storms and hurricanes form between June 1 and November 30. The United StatesNational Hurricane Center (NHC) monitors the basin and issues reports, watches and warnings abouttropical weather systems for the Atlantic Basin as one of theRegional Specialized Meteorological Centres fortropical cyclones as defined by theWorld Meteorological Organization.^[7] On average, 14 named storms (of tropical storm or higher strength) occur each season, with an average of 7 becoming hurricanes and 3 becoming major hurricanes. Theclimatological peak of activity is around September 10 each season.^[8]

The United States Atlantic coast and Gulf Coast,Mexico,Central America, theCaribbean Islands, andBermuda are frequently affected by storms in this basin. Venezuela, the 4 provinces ofAtlantic Canada, and AtlanticMacaronesian islands also are occasionally affected. Many of the more intense Atlantic storms areCape Verde-type hurricanes, which form off the west coast ofAfrica near theCape Verde islands. Occasionally, a hurricane that evolves into anextratropical cyclone can reach westernEurope, includingHurricane Gordon, which spread high winds across Spain and theBritish Isles in September 2006.^[9]Hurricane Vince, which made landfall on the southwestern coast of Spain as a tropical depression in October 2005, andSubtropical Storm Alpha, which made landfall on the coast of Portugal as a subtropical storm in September 2020, are the only known systems to impact mainland Europe as a (sub)tropical cyclone in the NHC study period commencing in 1851^[10] (it is believed a hurricane madelandfall in Spain in 1842).^[11]

The Northeastern Pacific is the second most active basin and has the highest number of storms per unit area. The hurricane season runs between May 15 and November 30 each year, and encompasses the vast majority of tropical cyclone activity in the region.^[12] In the 1971–2005 period, there were an average of 15–16 tropical storms, 9hurricanes, and 4–5 major hurricanes (storms ofCategory 3 intensity or greater) annually in the basin.^[12]

Storms that form here often affect westernMexico, and less commonly theContinental United States (in particularCalifornia), or northernCentral America. No hurricane included in the modern database has made landfall in California; however, historical records from 1858 speak of astorm that broughtSan Diego winds over 75 mph (65 kn; 121 km/h) (marginal hurricane force), though it is not known if the storm actually made landfall.^[13] Tropical storms in1939,1976,1997 and2023 brought gale-force winds to California.^[13]

TheCentral Pacific Hurricane Center'sarea of responsibility (AOR) begins at the boundary with theNational Hurricane Center's AOR (at 140 °W), and ends at the International Date Line, where the Northwestern Pacific begins.^[14] The hurricane season in the North Central Pacific runs annually from June 1 to November 30;^[15] The Central Pacific Hurricane Center monitors the storms that develop or move into the defined area of responsibility.^[14] The CPHC previously tasked with monitoring tropical activity in the basin was originally known as theJoint Hurricane Warning Center; today it is called theJoint Typhoon Warning Center.

Central Pacific hurricanes are rare and on average 4 to 5 storms form or move in this area annually.^[15] As there are no large contiguous landmasses in the basin, direct hits andlandfalls are rare; however, they occur occasionally, as withHurricane Iniki in 1992, which made landfall onHawaii,^[16] andHurricane Ioke in 2006, which made a direct hit onJohnston Atoll.^[17]

The Northwest Pacific Ocean, or Western North Pacific, is the most active basin on the planet, accounting for one third of all tropical cyclone activity. Annually, an average of 25.7 tropical cyclones in the basin acquiretropical storm strength or greater; also, an average of 16typhoons occurred each year during the 1968–1989 period.^{[6][needs update]} The basin occupies all the territory north of theequator and west of the International Date Line, including theSouth China Sea.^[14] The basin sees activity year-round; however, tropical activity is at its minimum in February and March.^[18]

Tropical storms in this region often affectChina,Hong Kong,Japan, theKoreas,Macau,Philippines,Taiwan andVietnam, plus numerousOceanian islands such asGuam, theNorthern Marianas andPalau. Sometimes, tropical storms in this region are powerful and long lasting enough to affect the more inland South East Asian nations ofLaos,Thailand, andCambodia, and in extreme cases, even the equatorial nations ofSingapore,Brunei,Malaysia, andIndonesia. The coast of China sees the most landfalling tropical cyclones worldwide.^[19] ThePhilippines receives an average of 6–7 tropical cyclone landfalls per year,^[20] with typhoonsHaiyan andGoni in 2013 and 2020 being the strongest and most powerful landfalling storms to date.^[21]

This basin is divided into two areas: theBay of Bengal and theArabian Sea, with the Bay of Bengal dominating (5 to 6 times more activity). Still, this basin is the least active worldwide, with only 4 to 6 storms per year.

This basin’s season has a double peak: one in April and May, before the onset ofthe monsoon, and another in October and November, just after.^[22] This double peak occurs because powerfulvertical wind shear in between the surface monsoonal low and upper tropospheric high during the monsoon season tears apart incipient cyclones.^[23] High shear explains why no cyclones can form in theRed Sea, which possesses the necessary depth, vorticity and surface temperatures year-round. Rarely do tropical cyclones that form elsewhere in this basin affect theArabian Peninsula orSomalia; however,Cyclone Gonu caused heavy damage in Oman on the peninsula in 2007.

Although the North Indian Ocean is a relatively inactive basin, extremely high population densities in theGanges andAyeyarwady Deltas mean that the deadliest tropical cyclones in the world have formed here, including the1970 Bhola cyclone, which killed 500,000 people. Nations affected includeIndia,Bangladesh,Sri Lanka,Thailand,Myanmar, andPakistan.

On rare occasions, tropical-like systems that can reach the intensity of hurricanes, occur over theMediterranean Sea. Such a phenomenon is called aMedicane (Mediterranean-hurricane). Although the geographical dimensions of tropicaloceans and theMediterranean Sea are clearly different, the precursor mechanisms of these perturbations, based on the air-sea thermodynamic imbalance, are similar.^[24] Their origins are typically non-tropical, and develop over open waters under strong, initially cold-corecyclones, similar to subtropical cyclones or anomalous tropical cyclones in the Atlantic Basin, likeKarl (1980),Vince (2005),Grace (2009),Chris (2012), orOphelia (2017).^[25]Sea surface temperatures in late-August and early-September are quite high over the basin (24/28 °C or 75/82 °F), though research indicates water temperatures of 20 °C (68 °F) are normally required for development.^[26]

Meteorological literature document that such systems occurred in September 1947, September 1969, January 1982, September 1983, January 1995, October 1996, September 2006, November 2011,November 2014, andNovember 2017.^[27][28] The 1995 system developed a well-definedeye, and a ship recorded 140 km/h (87 mph) winds, along with anatmospheric pressure of 975hPa. Although it had the structure of a tropical cyclone, it occurred over 16 °C (61 °F) water temperatures, suggesting it could have been apolar low.^[29]

Within theSouthern Hemisphere tropical cyclones generally form on a regular basis between the African coast and the middle of the South Pacific. Tropical and Subtropical Cyclones have also been noted occurring in the Southern Atlantic Ocean at times. For various reasons including where tropical cyclones form, there are several different ways to split the area between the American and African coasts. For instance theWorld Meteorological Organization define three different basins for the tracking and warning of tropical cyclones. These are the South-West Indian Ocean between the African Coast and 90°E, the Australian region between 90°E and 160°E and the South Pacific between 160°E and 120°W. The United StatesJoint Typhoon Warning Center also monitors the whole region, but splits it at 135°E into the South Pacific and the Southern Indian Ocean.

The South-West Indian Ocean is located within the Southern Hemisphere between the Africa's east coast and 90°E and is primarily monitored by the Meteo France's La Reunion RSMC, while the Mauritian, Australian, Indonesian, and Malagasy weather services also monitor parts of it.^[30] Until the start of the 1985–86 tropical cyclone season the basin only extended to 80°E, with the 10 degrees between 80 and 90E considered to be a part of the Australian region.^[31] On average about 9 cyclones per year develop into tropical storms, while 5 of those go on to become tropical cyclones that are equivalent to a hurricane or a typhoon.

Through the middle of 1985, this basin extended westward to 80°E. Since then, its western boundary has been 90°E.^[31] Tropical activity in this region affectsAustralia andIndonesia. According to the Australian Bureau of Meteorology, the most frequently hit portion of Australia is betweenExmouth andBroome inWestern Australia.^[32] The basin sees an average of about seven cyclones each year, although more can form or come in from other basins, such as the South Pacific.^[6][33][34] The tropical cycloneCyclone Vance in 1999 produced the highest recorded speed winds in an Australian town or city at around 267 km/h (166 mph).^[35]

The South Pacific Ocean basin runs between 160°E and 120°W, with tropical cyclones developing in it officially monitored by theFiji Meteorological Service and New Zealand'sMetService.^[5] Tropical Cyclones that develop within this basin generally affect countries to the west of the dateline, though during years of the warm phase ofEl Niño–Southern Oscillation cyclones have been known to develop to the east of the dateline near French Polynesia. On average the basin sees nine tropical cyclones annually with about half of them becoming severe tropical cyclones.

Cyclones rarely form in other tropical ocean areas, which are not formally considered tropical cyclone basins. Tropical depressions and tropical storms occur occasionally in thesouth Atlantic, and the only full-blown tropical cyclones on record were theAngola tropical storm in 1991,Hurricane Catarina in 2004,Tropical Storm Anita in 2010,Tropical Storm Iba in 2019,Tropical Storm 01Q in 2021 andTropical Storm Akará in 2024. The south Atlantic Ocean is not officially classified as a tropical cyclone basin by the World Meteorological Organization and does not have a designatedregional specialized meteorological center (RSMC). However, beginning in 2011, theBrazilian Navy Hydrographic Center started to assign names to tropical and subtropical systems in this basin, when they have sustained wind speeds of at least 65 km/h (40 mph).

• Regional Specialized Meteorological Centre
• Outline of tropical cyclones
• List of Atlantic–Pacific crossover hurricanes

• Tropical cyclones
• Tropical cyclone meteorology

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