Tropical cyclone basins

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Official tropical cyclone basins Tropical Cyclone Centers and Regions.png
Official tropical cyclone basins

Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the northern Pacific Ocean, the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean (Arabian Sea and Bay of Bengal). The western 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 of Category 3 intensity). [1]

Tropical cyclone Is a rotating storm system

A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".

Atlantic Ocean Ocean between Europe, Africa and the Americas

The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers. It covers approximately 20 percent of the Earth's surface and about 29 percent of its water surface area. It separates the "Old World" from the "New World".

Pacific Ocean Ocean between Asia and Australia in the west, the Americas in the east and Antarctica or the Southern Ocean in the south.

The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west and the Americas in the east.

Contents

Overview

Tropical cyclone basins and official warning centre.
BasinWarning CenterArea of responsibilityRefs
Northern Hemisphere
North Atlantic
Eastern Pacific
United States National Hurricane Center
United States Central Pacific Hurricane Center
Equator northward, African Coast – 140°W
Equator northward, 140°W-180
[2]
Western Pacific Japan Meteorological Agency Equator-60°N, 180-100°E [3]
North Indian Ocean India Meteorological Department Equator northward, 100°E-45°E
Southern Hemisphere
South-West Indian Ocean Meteo France ReunionEquator-40°S, African Coast-90°E [4]
Australian region Badan Meteorologi, Klimatologi, dan Geofisika
Papua New Guinea National Weather Service
Australian Bureau of Meteorology
Equator-10°S, 90°E-141°E
Equator-10°S, 141°E-160°E
10°S-36°S, 90°E-160°E
[5]
Southern Pacific Fiji Meteorological Service
Meteorological Service of New Zealand
Equator-25°S, 160°E-120°W
25°S-40°S, 160°E-120°W
[5]

Northern Hemisphere

North Atlantic Ocean

Tracks of all tropical cyclones in the northern Atlantic Ocean between 1980 and 2005 Atlantic hurricane tracks 1980-2005.jpg
Tracks of all tropical cyclones in the northern Atlantic Ocean between 1980 and 2005

This region includes the North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. Tropical cyclone formation here varies widely from year to year, ranging from one to over twenty-five per year. [6] Most Atlantic tropical storms and hurricanes form between June 1 and November 30. The United States National Hurricane Center (NHC) monitors the basin and issues reports, watches and warnings about tropical weather systems for the Atlantic Basin as one of the Regional Specialized Meteorological Centres for tropical cyclones as defined by the World Meteorological Organization. [7] On average, 11 named storms (of tropical storm or higher strength) occur each season, with an average of 6 becoming hurricanes and 2 becoming major hurricanes. The climatological peak of activity is around September 10 each season. [8]

Caribbean Sea A sea of the Atlantic Ocean bounded by North, Central, and South America

The Caribbean Sea is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico and Central America to the west and south west, to the north by the Greater Antilles starting with Cuba, to the east by the Lesser Antilles, and to the south by the north coast of South America.

Gulf of Mexico An Atlantic Ocean basin extending into southern North America

The Gulf of Mexico is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. The U.S. states of Texas, Louisiana, Mississippi, Alabama, and Florida border the Gulf on the north, which are often referred to as the "Third Coast", in comparison with the U.S. Atlantic and Pacific coasts.

National Hurricane Center division of the United States National Weather Service

The National Hurricane Center (NHC) is the division of the United States' National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 30th parallel north in the northeast Pacific Ocean and the 31st parallel north in the northern Atlantic Ocean. The agency, which is co-located with the Miami branch of the National Weather Service, is situated on the campus of Florida International University in University Park, Florida.

The United States Atlantic coast and Gulf Coast, Mexico, Central America, the Caribbean Islands, and Bermuda are frequently affected by storms in this basin. Venezuela, the 4 provinces of Atlantic Canada, and Atlantic Macaronesian islands also are occasionally affected. 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. Occasionally, a hurricane that evolves into an extratropical cyclone can reach western Europe, including Hurricane Gordon, which spread high winds across Spain and the British Isles in September 2006. [9] Hurricane Vince, which made landfall on the southwestern coast of Spain as a tropical depression in October 2005, is the only known system to impact mainland Europe as a tropical cyclone in the NHC study period commencing in 1851 [10] (it is believed a hurricane made landfall in Spain in 1842). [11]

Mexico Country in the southern portion of North America

Mexico, officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatemala, Belize, and the Caribbean Sea; and to the east by the Gulf of Mexico. Covering almost 2,000,000 square kilometres (770,000 sq mi), the nation is the fifth largest country in the Americas by total area and the 13th largest independent state in the world. With an estimated population of over 120 million people, the country is the tenth most populous state and the most populous Spanish-speaking state in the world, while being the second most populous nation in Latin America after Brazil. Mexico is a federation comprising 31 states and Mexico City, a special federal entity that is also the capital city and its most populous city. Other metropolises in the state include Guadalajara, Monterrey, Puebla, Toluca, Tijuana and León.

Central America central geographic region of the Americas

Central America is located on the southern tip of North America, or is sometimes defined as a subcontinent of the Americas, bordered by Mexico to the north, Colombia to the southeast, the Caribbean Sea to the east, and the Pacific Ocean to the west and south. Central America consists of seven countries: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama. The combined population of Central America has been estimated to be 41,739,000 and 42,688,190.

Bermuda British overseas territory in the North Atlantic Ocean

Bermuda is a British Overseas Territory in the North Atlantic Ocean. It is approximately 1,070 km (665 mi) east-southeast of Cape Hatteras, North Carolina; 1,236 km (768 mi) south of Cape Sable Island, Nova Scotia; and 1,759 km (1,093 mi) northeast of Cuba. The capital city is Hamilton. Bermuda is self-governing, with its own constitution and its own government, which enacts local laws, while the United Kingdom retains responsibility for defence and foreign relations. As of July 2018, its population is 71,176, the highest of the British overseas territories.

Northeastern Pacific Ocean

Tracks of all tropical cyclones in the northern Pacific Ocean east of the International Date Line between 1980 and 2005; the vertical line through the center separates the Central Pacific basin (under the Central Pacific Hurricane Center's watch) from the Northeastern Pacific basin (under the National Hurricane Center's area of responsibility). Pacific hurricane tracks 1980-2005.jpg
Tracks of all tropical cyclones in the northern Pacific Ocean east of the International Date Line between 1980 and 2005; the vertical line through the center separates the Central Pacific basin (under the Central Pacific Hurricane Center's watch) from the Northeastern Pacific basin (under the National Hurricane Center's area of responsibility).

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, 9 hurricanes, and 4–5 major hurricanes (storms of Category 3 intensity or greater) annually in the basin. [12]

Storms that form here often affect western Mexico, and less commonly the Continental United States (in particular California), or northern Central America. No hurricane included in the modern database has made landfall in California; however, historical records from 1858 speak of a storm that brought San 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 in 1939, 1976 and 1997 brought gale-force winds to California. [13]

California State of the United States of America

California is a state in the Pacific Region of the United States. With 39.6 million residents, California is the most populous U.S. state and the third-largest by area. The state capital is Sacramento. The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and fifth-most populous urban regions, with 18.7 million and 9.7 million residents respectively. Los Angeles is California's most populous city, and the country's second-most populous, after New York City. California also has the nation's most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The City and County of San Francisco is both the country's second-most densely populated major city after New York City and the fifth-most densely populated county, behind only four of the five New York City boroughs.

San Diego City in California, United States

San Diego is a city in the U.S. state of California. It is in San Diego County, on the coast of the Pacific Ocean in Southern California, approximately 120 miles (190 km) south of Los Angeles and immediately adjacent to the border with Mexico.

Hurricane Kathleen (1976) Category 1 Pacific hurricane in 1976

Hurricane Kathleen was a tropical cyclone that had a destructive impact in California. On September 7, 1976, a tropical depression formed; two days later it accelerated north towards the Baja California Peninsula. Kathleen brushed the Pacific coast of the peninsula as a hurricane on September 9 and made landfall as a fast-moving tropical storm the next day. With its circulation intact and still a tropical storm, Kathleen headed north into the United States and affected California and Arizona. Kathleen finally dissipated late on September 11.

The Central Pacific Hurricane Center's area of responsibility (AOR) begins at the boundary with the National Hurricane Center' 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 the Joint Hurricane Warning Center; today it is called the Joint Typhoon Warning Center.

Central Pacific Hurricane Center

The Central Pacific Hurricane Center (CPHC) of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central Pacific region: from the equator northward, 140°W–180°W, most significantly for Hawai‘i. It is the Regional Specialized Meteorological Center (RSMC) for tropical cyclones in this region, and in this capacity is known as RSMC Honolulu.

Area of Responsibility (AOR) is a pre-defined geographic region assigned to Combatant commanders of the Unified Command Plan (UCP), that are used to define an area with specific geographic boundaries where they have the authority to plan and conduct operations; for which a force, or component commander bears a certain responsibility. The term may also be used in other countries worldwide but it originated within the United States Armed Forces. This system is designed to allow a single commander to exercise command and control of all military forces in the AOR, regardless of their branch of service.

Longitude A geographic coordinate that specifies the east-west position of a point on the Earths surface

Longitude, is a geographic coordinate that specifies the east–west position of a point on the Earth's surface, or the surface of a celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians connect points with the same longitude. By convention, one of these, the Prime Meridian, which passes through the Royal Observatory, Greenwich, England, was allocated the position of 0° longitude. The longitude of other places is measured as the angle east or west from the Prime Meridian, ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. Specifically, it is the angle between a plane through the Prime Meridian and a plane through both poles and the location in question.

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 and landfalls are rare; however, they occur occasionally, as with Hurricane Iniki in 1992, which made landfall on Hawaii, [16] and Hurricane Ioke in 2006, which made a direct hit on Johnston Atoll. [17]

Northwestern Pacific Ocean

Tracks of all tropical cyclones in the northwestern Pacific Ocean between 1980 and 2005. The vertical line to the right is the International Date Line. Pacific typhoon tracks 1980-2005.jpg
Tracks of all tropical cyclones in the northwestern Pacific Ocean between 1980 and 2005. The vertical line to the right is the International Date Line.

The Northwest Pacific Ocean 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 acquire tropical storm strength or greater; also, an average of 16 typhoons occurred each year during the 1968–1989 period. [6] The basin occupies all the territory north of the equator and west of the International Date Line, including the South 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 affect China, Hong Kong, Macau, Japan, Korea, Philippines, Taiwan and Vietnam, plus numerous Oceanian islands such as Guam, the Northern Marianas and Palau. Sometimes, tropical storms in this region affect Laos, Thailand, Cambodia and even Singapore, Malaysia and Indonesia. The coast of China sees the most landfalling tropical cyclones worldwide. [19] The Philippines receives an average of 6–7 tropical cyclone landfalls per year, [20] with Super Typhoon Haiyan being the strongest and most powerful to date since its landfall in November 8, 2013. [21]

North Indian Ocean

Tracks of all tropical cyclones in the northern Indian Ocean between 1980 and 2005 North Indian Ocean cyclone tracks 1980-2005.jpg
Tracks of all tropical cyclones in the northern Indian Ocean between 1980 and 2005

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). 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 of the monsoon, and another in October and November, just after. [22] This double peak occurs because powerful vertical 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 the Red Sea, which possesses the necessary depth, vorticity and surface temperatures year-round. Rarely do tropical cyclones that form elsewhere in this basin affect the Arabian Peninsula or Somalia; 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 the Ganges and Ayeyarwady Deltas mean that the deadliest tropical cyclones in the world have formed here, including the 1970 Bhola cyclone, which killed 500,000 people. Nations affected include India, Bangladesh, Sri Lanka, Thailand, Myanmar, and Pakistan.

Mediterranean Sea

Image of the January 1995 system Mediterranean Hurricane 16 Jan 1995.jpg
Image of the January 1995 system

On rare occasions, tropical-like systems that can reach the intensity of hurricanes, occur over the Mediterranean Sea. Such a phenomenon is called a Medicane (Mediterranean-hurricane). Although the geographical dimensions of tropical oceans and the Mediterranean 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-core cyclones, similar to subtropical cyclones or anomalous tropical cyclones in the Atlantic Basin, like Karl (1980), Vince (2005), Grace (2009), Chris (2012), or Ophelia (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, and November 2017. [27] [28] The 1995 system developed a well-defined eye, and a ship recorded 85 mph (140 km/h) winds, along with an atmospheric pressure of 975 mbar. Although it had the structure of a tropical cyclone, it occurred over 61 °F (16 °C) water temperatures, suggesting it could have been a polar low. [29]

Southern Hemisphere

Within the Southern 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 the World 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 States Joint Typhoon Warning Center also monitors the whole region, but splits it at 135°E into the South Pacific and the Southern Indian Ocean.

South-West Indian Ocean

Tracks of all tropical cyclones in the southwestern Indian Ocean between 1980 and 2005 Southwest Indian Ocean cyclone tracks 1980-2005.jpg
Tracks of all tropical cyclones in the southwestern Indian Ocean between 1980 and 2005

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. [32] The tropical cyclones that form in this area can affect some of the various Indian Ocean island nations and or various countries along Africa's east coast.

Australian region

Tracks of all tropical cyclones in the southeastern Indian Ocean between 1980 and 2005 Southeast Indian Ocean cyclone tracks 1980-2005.jpg
Tracks of all tropical cyclones in the southeastern Indian Ocean between 1980 and 2005

Through the middle of 1985, this basin extended westward to 80E. Since then, its western boundary has been 90E. [31] Tropical activity in this region affects Australia and Indonesia. According to the Australian Bureau of Meteorology, the most frequently hit portion of Australia is between Exmouth and Broome in Western Australia. [33] 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] [34] [35] The tropical cyclone Cyclone Vance in 1999 produced the highest recorded speed winds in an Australian town or city at around 267 km/h (166 mph). [36]

South Pacific Ocean

Tracks of all tropical cyclones in the southwestern Pacific Ocean between 1980 and 2005 South Pacific cyclone tracks 1980-2005.jpg
Tracks of all tropical cyclones in the southwestern Pacific Ocean between 1980 and 2005

The South Pacific Ocean basin runs between 160°E and 120°W, with tropical cyclones developing in it officially monitored by the Fiji Meteorological Service and New Zealand's MetService. [37] Tropical Cyclones that develop within this basin generally affect countries to the west of the dateline, though during years of the warm phase of El 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.

South Atlantic Ocean

Hurricane Catarina is currently the only known tropical cyclone in the South Atlantic Ocean to have actually reached hurricane intensity. Catarina 27 mar 2004 1630Z.jpg
Hurricane Catarina is currently the only known tropical cyclone in the South Atlantic Ocean to have actually reached hurricane intensity.

Cyclones rarely form in other tropical ocean areas, which are not formally considered tropical cyclone basins. Tropical depressions and tropical storms occur occasionally in the South Atlantic, and the only full-blown tropical cyclones on record were 2004's Hurricane Catarina, which made landfall in Brazil and 2010's Tropical Storm Anita, which formed off the coast of Rio Grande do Sul. The South Atlantic Ocean is not officially classified as a tropical cyclone basin by the World Meteorological Organization and does not have a designated regional specialized meteorological center (RSMC). However, beginning in 2011, the Brazilian 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).

See also

Related Research Articles

Tropical cyclones and subtropical cyclones are named by various warning centers to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings. The names are intended to reduce confusion in the event of concurrent storms in the same basin. Generally once storms produce sustained wind speeds of more than 33 knots, names are assigned in order from predetermined lists depending on which basin they originate. However, standards vary from basin to basin: some tropical depressions are named in the Western Pacific, while tropical cyclones must have a significant amount of gale-force winds occurring around the centre before they are named in the Southern Hemisphere.

Tropical cyclone warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate preparation for the cyclone, including evacuation of vulnerable areas where necessary. It is important that interests throughout the area of an alert make preparations to protect life and property, and do not disregard it on the strength of the detailed forecast track. Tropical cyclones are not points, and forecasting their track remains an uncertain science.

Pacific hurricane mature tropical cyclone that develops within the eastern and central Pacific Ocean

A Pacific hurricane is a mature tropical cyclone that develops within the eastern and central Pacific Ocean to the east of 180°W, north of the equator. For tropical cyclone warning purposes, the northern Pacific is divided into three regions: the eastern, central, and western, while the southern Pacific is divided into 2 sections, the Australian region and the southern Pacific basin between 160°E and 120°W. Identical phenomena in the western north Pacific are called typhoons. This separation between the two basins has a practical convenience, however, as tropical cyclones rarely form in the central north Pacific due to high vertical wind shear, and few cross the dateline.

Typhoon type of tropical cyclone when is located i northwest Pacific. Classified by JMA typhoons wind scale and JTWC typhoons wind scale

A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for almost one-third of the world's annual tropical cyclones. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, central, and western. The Regional Specialized Meteorological Center (RSMC) for tropical cyclone forecasts is in Japan, with other tropical cyclone warning centers for the northwest Pacific in Hawaii, the Philippines and Hong Kong. While the RSMC names each system, the main name list itself is coordinated among 18 countries that have territories threatened by typhoons each year A hurricane is a storm that occurs in the Atlantic Ocean or the northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a tropical cyclone occurs in the South Pacific or the Indian Ocean.

Tropical cyclones are unofficially ranked on one of five tropical cyclone intensity scales, according to their maximum sustained winds and which tropical cyclone basin(s) they are located in. Only a few scales of classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but some alternative scales also exist, such as accumulated cyclone energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.

Atlantic hurricane tropical cyclone that forms in the North Atlantic Ocean

An Atlantic hurricane or tropical storm is a tropical cyclone that forms in the Atlantic Ocean, usually between the months of June and November. A hurricane differs from a cyclone or typhoon only on the basis of location. A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean.

Tropical cyclogenesis

Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.

An Australian region tropical cyclone is a non-frontal, low pressure system that has developed, within an environment of warm sea surface temperatures and little vertical wind shear aloft in either the Southern Indian Ocean or the South Pacific Ocean. Within the Southern Hemisphere there are officially three areas where tropical cyclones develop on a regular basis, these areas are the South-West Indian Ocean between Africa and 90°E, the Australian region between 90°E and 160°E and the South Pacific basin between 160°E and 120°W. The Australian region between 90°E and 160°E is officially monitored by the Australian Bureau of Meteorology, the Papua New Guinea National Weather Service and the Indonesian Agency for Meteorology, Climatology and Geophysics, while others like the Fiji Meteorological Service and the United States National Oceanic and Atmospheric Administration also monitor the basin. Each tropical cyclone year within this basin starts on 1 July and runs throughout the year, encompassing the tropical cyclone season which runs from 1 November and lasts until 30 April each season. Within the basin, most tropical cyclones have their origins within the South Pacific Convergence Zone or within the Northern Australian monsoon trough, both of which form an extensive area of cloudiness and are dominant features of the season. Within this region a tropical disturbance is classified as a tropical cyclone, when it has 10-minute sustained wind speeds of more than 65 km/h (35 mph), that wrap halfway around the low level circulation centre, while a severe tropical cyclone is classified when the maximum 10-minute sustained wind speeds are greater than 120 km/h (75 mph).

South-West Indian Ocean tropical cyclone type of tropical cyclone located in South West Indian Ocean and measured by Météo-France La Reunion scale

In the south-west Indian Ocean, tropical cyclones form south of the equator and west of 90° E to the coast of Africa.

1984 North Indian Ocean cyclone season

The 1984 North Indian Ocean cyclone season was part of the annual cycle of tropical cyclone formation. The season has no official bounds but cyclones tend to form between April and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northern Indian Ocean. There are two main seas in the North Indian Ocean—the Bay of Bengal to the east of the Indian subcontinent and the Arabian Sea to the west of India. The official Regional Specialized Meteorological Centre in this basin is the India Meteorological Department (IMD), while the Joint Typhoon Warning Center (JTWC) releases unofficial advisories. An average of five tropical cyclones form in the North Indian Ocean every season with peaks in May and November. Cyclones occurring between the meridians 45°E and 100°E are included in the season by the IMD.

Tropical cyclones of 2010 were spread across seven oceanic basins in their respective seasons; the strongest of these tropical cyclones was Typhoon Megi, which strengthened to a minimum barometric pressure of 885 mbar before striking the east coast of Luzon in the Philippines. Regional Specialized Meteorological Centers (RSMC) and Tropical Cyclone Warning Centers (TCWC) designated names to 70 systems worldwide, of which 46 occurred in the northern hemisphere while 21 developed in the southern hemisphere. The most active basin in 2010 was the North Atlantic, which documented 19 named systems, while the North Indian Ocean, despite only amounting to five named systems, was its basin's most active since 1998. Conversely, both the West Pacific typhoon and East Pacific hurricane seasons experienced the least number of cyclones reaching tropical storm intensity in recorded history, numbering 14 and 8, respectively. Activity across the southern hemisphere's three basins—South-West Indian, Australian, and South Pacific—was spread evenly, with each region recording seven named storms apiece. That hemisphere's strongest tropical cyclone was Cyclone Edzani, which bottomed out with a barometric pressure of 910 mbar in the South-West Indian Ocean.

The 2019 Pacific hurricane season is an upcoming event in the annual cycle of tropical cyclone formation, in which tropical cyclones form in the eastern Pacific Ocean. The season will officially begin on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they will both end on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. However, the formation of tropical cyclones is possible at any time of the year.

Tropical cyclones in 2015

Tropical cyclones in 2015 were spread out across seven different areas called basins; the strongest of these tropical cyclones was Hurricane Patricia, which strengthened to a minimum barometric pressure of 872 mbar before striking the east coast of Colima in Mexico. 133 tropical cyclones had formed this year to date. 92 tropical cyclones had been named by either a Regional Specialized Meteorological Center (RSMC) or a Tropical Cyclone Warning Center (TCWC).

Tropical cyclones in 2019 are spread out across seven different areas called basins and the Mediterranean Sea. Currently, 39 systems have formed during the year to date. 24 tropical cyclones have been named by either a Regional Specialized Meteorological Center (RSMC) or a Tropical Cyclone Warning Center (TCWC).

Tropical cyclones in 2014

Tropical cyclones in 2014 were spread out across seven different areas called basins; the strongest of these tropical cyclones was Typhoon Vongfong, which strengthened to a minimum barometric pressure of 900 mbar before striking the east coast of Japan. 119 tropical cyclones had formed this year to date. 82 tropical cyclones had been named by either a Regional Specialized Meteorological Center (RSMC) or a Tropical Cyclone Warning Center (TCWC). The most active basin in 2014 was the Western Pacific, which documented 23 named systems, while the Eastern Pacific, despite only amounting to 22 named systems, was its basin's most active since 1992. Conversely, both the North Atlantic hurricane and North Indian Ocean cyclone seasons experienced the least number of cyclones reaching tropical storm intensity in recorded history, numbering 9 and 3, respectively. Activity across the southern hemisphere's three basins—South-West Indian, Australian, and South Pacific—was spread evenly, with each region recording seven named storms apiece.

Tropical cyclones in 2004 were spread out across seven different areas called basins; the strongest of these tropical cyclones was Cyclone Gafilo, which strengthened to a minimum barometric pressure of 895 mbar becomes the most intense tropical cyclone ever recorded in the South-West Indian Ocean before striking the east coast of Madagascar. 130 tropical cyclones had formed this year to date. 81 tropical cyclones had been named by either a Regional Specialized Meteorological Center (RSMC) or a Tropical Cyclone Warning Center (TCWC). The most active basin in 2004 was the Western Pacific, which documented 29 named systems, while the North Atlantic, despite only amounting to 15 named systems, was its basin's hyperactive season since 1995. Conversely, both the Eastern Pacific hurricane and North Indian Ocean cyclone seasons experienced the least number of cyclones reaching tropical storm intensity in recorded history, numbering 12 and 4, respectively. Activity across the southern hemisphere's three basins—South-West Indian, Australian, and South Pacific—was spread evenly, with each region recording seven named storms apiece.

Tropical cyclones in 2012

Tropical cyclones in 2012 were spread out across seven different areas called basins; the strongest tropical cyclone was Typhoon Sanba strengthened to a minimum barometric pressure of 900 mbar before striking South Korea. 132 tropical cyclones had formed this year to date. 88 tropical cyclones had been named by either a Regional Specialized Meteorological Center (RSMC) or a Tropical Cyclone Warning Center (TCWC). The most active basin in the year was the Western Pacific, which documented 25 named systems, while the North Atlantic Pacific, despite only amounting to 19 named systems, was its basin's hyperactive since 2010 becoming the third-most active season on record. Conversely, the Eastern Pacific hurricane season experienced the average number of cyclones reaching tropical storm intensity, numbering 17 respectively. The least tropical cyclone season was North Indian Ocean had a late start, with the first system forming in October. Activity across the southern hemisphere's three basins—South-West Indian, Australian, and South Pacific—was spread evenly, with each region recording seven named storms apiece.

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