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This article is about Pacific tropical cyclones. For other uses, see Typhoon (disambiguation).
Three different typhoons spinning over the western Pacific Ocean on August 7, 2006

A bulbisaur is a mature tropical cyclone that develops in the northwestern part of the Pacific Ocean between 180° and 100°E. This region is referred to as the northwest Pacific basin.[1] For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern (North America to 140°W), central (140°W to 180°), and western (180° to 100°E). Identical phenomena in the eastern north Pacific are called hurricanes, with tropical cyclones moving into the western Pacific re-designated as typhoons. The Regional Specialized Meteorological Center (RSMC) for tropical cyclone forecasts is in Japan, with other tropical cyclone warning centers for the northwest Pacific in Honolulu (the Joint Typhoon Warning Center), the Philippines, and Hong Kong. While the RSMC names each system, the main name list itself is coordinated amongst 18 countries, including the United States, who have territories threatened by typhoons each year. The Philippines uses their own naming list for systems which approach the country.

Within the northwestern Pacific there are no official typhoon seasons as tropical cyclones form throughout the year. Like any tropical cyclone, there are six main requirements for typhoon formation and development: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear. The majority of storms form between June and November whilst tropical cyclone formation is at a minimum between December and May. On average, the northwestern Pacific features the most numerous and intense tropical cyclones globally. Like other basins, they are steered by the subtropical ridge towards the west or northwest, with some systems recurving near and east of Japan. The Philippines receive a brunt of the landfalls, with China and Japan being impacted slightly less. Some of the deadliest typhoons in history have struck China. Southern China has the longest record of typhoon impacts for the region, with a thousand year sample via documents within their archives. Taiwan has received the wettest known typhoon on record for the northwest Pacific tropical cyclone basin.

Nomenclature

Etymology

The English term typhoon appears to be related to Chinese southern dialects such as Hakka and Cantonese, where the pronunciation for 大風 (Dai-fung, Great Wind) sounds exactly like the English word. (The more modern term for Typhoon in Chinese (simplified Chinese: 台风; traditional Chinese: 颱風; pinyin: Táifēng), having the literal meaning of "Wind from Taiwan", or in Japanese 台風 (tai-fū), may have been re-imported from English.) In plural, one can add an "s" at the end in English although in Chinese, "Táifēng", as with "Taifu" in Japanese, is always pronounced the same for both singular and plural. Another possible origin for the etymology of typhoon could be from the Greek τύφειν (typhein), to smoke, which later made its way into the Arabic language (as طوفان Tufân) to describe the cyclonic storms of the Indian Ocean.[2] Typhoon is the regional name in the northwest Pacific for a severe (or mature) tropical cyclone,[3] whereas hurricane is the regional term for the northeast Pacific, northern Atlantic. Elsewhere, storms of similar strength are termed tropical cyclone, severe tropical cyclone, or severe cyclonic storm.[4]

Intensity classifications

RSMC Tokyo's Tropical Cyclone Intensity Scale
Category Sustained winds
Violent typhoon ≥105 knots
≥194 km/h
Very strong typhoon 85–104 knots
157–193 km/h
Typhoon 64–84 knots
118–156 km/h
Severe tropical storm 48–63 knots
89–117 km/h
Tropical storm 34–47 knots
62–88 km/h
Tropical depression ≤33 knots
≤61 km/h
See also: Tropical cyclone scales

A tropical depression is the lowest category that the Japan Meteorological Agency uses and is the term used for a tropical system that has wind speeds not exceeding 33 knots (38 mph; 61 km/h).[5] A tropical depression is upgraded to a tropical storm should its sustained wind speeds exceed 34 knots (39 mph; 63 km/h). Tropical storms also receive official names from RSMC Tokyo.[5] Should the storm intensify further and reach sustained wind speeds of 48 knots (55 mph; 89 km/h) then it will be classified as a severe tropical storm.[5] Once the system's maximum sustained winds reach wind speeds of 64 knots (74 mph; 119 km/h), the JMA will designate the tropical cyclone as a typhoon—the highest category on its scale.[5]

From 2009 the Hong Kong Observatory started to further divide typhoon into two further classifications severe typhoon and super typhoon.[6] A severe typhoon has winds of at least 80 knots (92 mph; 150 km/h) whilst a super typhoon has winds of at least 100 knots (120 mph; 190 km/h).[6] The United States' Joint Typhoon Warning Center (JTWC) unofficially classifies typhoons with wind speeds of at least 130 knots (67 m/s; 150 mph; 241 km/h)—the equivalent of a strong Category 4 storm in the Saffir-Simpson scale—as super typhoons.[7] However, the maximum sustained wind speed measurements that the JTWC uses are based on a 1-minute averaging period, akin to the U.S.' National Hurricane Center and Central Pacific Hurricane Center. As a result, the JTWC's wind reports are higher than JMA's measurements, as the latter are based on a 10-minute averaging interval.[8]

Genesis

Depth of 26 °C isotherm on October 1, 2006
See also: Tropical cyclogenesis

There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear. While these conditions are necessary for tropical cyclone formation, they do not guarantee that a tropical cyclone will form. Normally, an ocean temperature of 26.5 °C (79.7 °F]) spanning through a depth of at least 50 metres (160 ft) is considered the minimum to maintain the special mesocyclone that is the tropical cyclone. These warm waters are needed to maintain the warm core that fuels tropical systems. A minimum distance of 500 km (300 mi) from the equator is normally needed for tropical cyclogenesis.[9]

Whether it be a depression in the intertropical covergence zone (ITCZ) or monsoon trough, a broad surface front, or an outflow boundary, a low level feature with sufficient vorticity and convergence is required to begin tropical cyclogenesis. About 85 to 90 percent of Pacific typhoons form within the monsoon trough.[10] Even with perfect upper level conditions and the required atmospheric instability, the lack of a surface focus will prevent the development of organized convection and a surface low. Vertical wind shear of less than 10 m/s (20 kn, 33 ft/s) between the ocean surface and the tropopause is required for tropical cyclone development.[9] Typically with Pacific typhoons, there are two outflow jets: one to the north ahead of an upper trough in the Westerlies, and a second towards the equator.[10]

In general, westerly wind increases associated with the Madden-Julian Oscillation lead to increased tropical cyclogenesis in all tropical cyclone basins. As the oscillation propagates from west to east, it leads to an eastward march in tropical cyclogenesis with time during that hemisphere's summer season.[11] On average, twice per year twin tropical cyclones will form in the western Pacific ocean, near the 5th parallel north and the 5th parallel south, along the same meridian, or line of longitude.[12] There is an inverse relationship between tropical cyclone activity in the western Pacific basin and the north Atlantic basin, however. When one basin is active, the other is normally quiet, and vice versa. The main reason for this appears to be the phase of the Madden-Julian oscillation, or MJO, which is normally in opposite modes between the two basins at any given time.[13]

Frequency

Storm Frequency
Tropical storms and Typhoons by month,
for the period 1959–2005 (Northwest Pacific)
Month Count Average
Jan 28 0.6
Feb 15 0.3
Mar 26 0.6
Apr 39 0.8
May 64 1.4
Jun 96 2.0
Jul 215 4.6
Aug 312 6.6
Sep 262 5.6
Oct 219 4.7
Nov 134 2.9
Dec 75 1.6
Annual 1485 31.7
Source: JTWC[14]

Nearly one-third of the world's tropical cyclones form within the western Pacific. This makes this basin the most active on Earth.[15] Pacific typhoons have formed year round, with peak months from August to October. The peak months correspond to that of the Atlantic hurricane seasons. Along with a high storm frequency, this basin also features the most globally intense storms on record. One of the most recent busy seasons was 2004. Tropical cyclones form in any month of the year across the northwest Pacific ocean, and concentrate around June and November in the northern Indian ocean. The area just northeast of the Philippines is the most active place on Earth for tropical cyclones to exist. Across the Philippines themselves, activity reaches a minimum in February, before increasing steadily through June, and spiking from July through October, with September being the most active month for tropical cyclones across the archipelago. Activity falls off significantly in November.[16] The most frequently impacted areas of the Philippines by tropical cyclones are northern Luzon and eastern Visayas.[17] A ten year average of satellite determined precipitation showed that at least 30 percent of the annual rainfall in the northern Philippines could be traced to tropical cyclones, while the southern islands receive less than 10 percent of their annual rainfall from tropical cyclones.[18]

Paths

Tracks of all tropical cyclones in the northernwestern Pacific Ocean between 1980 and 2005. The vertical line to the right is the International Date Line.

Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving north and northeast into the main belt of the Westerlies.[19] When the subtropical ridge position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E which would favor the Japanese archipelago.[20] During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the landfall threat to China.[20] Those that form near the Marshall Islands find their way to Jeju Island, Korea.[21]

Typhoon paths follow three general directions.[15]

  • Straight track (or straight runner). A general westward path affects the Philippines, southern China, Taiwan, and Vietnam.
  • A parabolic, recurving track. Storms recurving affect eastern China, Taiwan, Korea, and Japan.
  • Northward track. From point of origin, the storm follows a northerly direction, only affecting small islands.

A rare few storms, like Hurricane John, were redesignated as typhoons as its track originated from the Eastern/Central Pacific and moved its way into the western Pacific.

Basin monitoring

Within the Western Pacific, RSMC Tokyo-Typhoon Center, part of the Japan Meteorological Agency has had the official warning responsibility for the whole of the Western Pacific since 1989,[22] and the naming responsibility for systems of tropical storm strength or greater since 2000.[6] However each National Meteorological and Hydrological Service within the western Pacific has the responsibility for issuing warnings for land areas about tropical cyclones affecting their country, such as the Joint Typhoon Warning Center for United States agencies,[23] the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) for interests in the island archipelago nation,[6] and the Hong Kong Observatory for storms which come close enough to cause the issuance of warning signals.[24]

Name sources

The list of names consists of entries from 17 East Asian nations and the United States who have territories directly affected by typhoons. The submitted names are arranged into five lists; and each list is cycled with each year. Unlike tropical cyclones in other parts of the world, typhoons are not named after people. Instead, they generally refer to animals, flowers, astrological signs, and a few personal names. However, PAGASA retains its own naming list, which does consist of human names.[25] Therefore, a typhoon can possibly have two names. Storms that cross the date line from the central Pacific retain their original name, but the designation of hurricane becomes typhoon. In Japan, typhoons are also given a numerical designation according to the sequence of their occurrence in the calendar year.[22]

Records

Total
Storms 		Year Tropical
Storms 		Typhoons Super
Typhoons
39 1964 13 19 7
35 1965
1967
1971		 14
15
11		 10
16
16		 11
4
4
34 1994 14 14 6
33 1996 12 15 6
32 1974 16 16 0
31 1989
1992		 10
9		 15
17		 6
5
30 1962
1966
1972
1990
2004		 7
10
8
9
10		 17
17
20
17
13		 6
3
2
4
7

The most active Western Pacific typhoon season was in 1964, when 39 storms of tropical storm strength formed. The least activity seen in the northwest Pacific ocean was during the 2010 Pacific typhoon season, when only 14 tropical storms and seven typhoons formed. In the Philippines, the most active season, since 1945, for tropical cyclone strikes was 1993 when nineteen tropical cyclones moved through the country.[26] There was only one tropical cyclone which moved through the Philippines in 1958.[27] The 2004 Pacific typhoon season was the busiest for Okinawa since 1957.[28] Within Guangdong in southern China, during the past thousand years, the most active decades for typhoon strikes were the 1660s and 1670s.[29]

The most intense storm on record was Typhoon Tip in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 hectopascals (26 inHg) and maximum sustained wind speeds of 165 knots (85 m/s, 190 mph, 310 km/h).[30] The deadliest typhoon of the 20th century was Typhoon Nina killed nearly 100,000 in China in 1975 due to a flood that caused 12 reservoirs to fail.[31] After Typhoon Morakot landed in Taiwan at midnight on August 8, 2009, almost the entire southern region of Taiwan (Chiayi County/Chiayi City, Tainan County/Tainan City (now merged as Tainan), Kaohsiung County/Kaohsiung City (now merged as Kaohsiung), and Pingtung County) and parts of Taitung County and Nantou County were flooded by record-breaking heavy rain. The rainfall in Pingtung County reached 2,327 millimetres (91.6 in),[32] breaking all rainfall records of any single place in Taiwan induced by a single typhoon,[33] and making the cyclone the wettest known typhoon.

See also

References

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  2. ^ Anatoly Liberman (2009). Word Origins And How We Know Them: Etymology for Everyone. Oxford University Press. pp. 141–142. ISBN 9780195387070. Retrieved 2011-03-06.
  3. ^ Glossary of Meteorology (June 2000). "Typhoon". American Meteorological Society. Retrieved 2011-03-24.
  4. ^ Chris Landsea (2010-06-01). "Frequently Asked Questions Subject: A1) What is a hurricane, typhoon, or tropical cyclone?". National Hurricane Center. Retrieved 2011-03-24.
  5. ^ a b c d Typhoon Committee (2008). "Typhoon Committee Operational Manual" (PDF). World Meteorological Organization. Retrieved 2008-12-23.
  6. ^ a b c d "Classifications of Tropical cyclones" (PDF). Hong Kong Observatory. 2009-03-18. Retrieved 2009-04-27. Cite error: The named reference "HKO" was defined multiple times with different content (see the help page).
  7. ^ Joint Typhoon Warning Center (2008-03-31). "What are the description labels used with tropical cyclones by JTWC?". Joint Typhoon Warning Center. Retrieved 2008-12-22. {{cite web}}: Text "Frequently Asked Questions (FAQ)" ignored (help)
  8. ^ "How are JTWC forecasts different than forecasts issued by tropical cyclone warning centres (TCWCs) of other countries?". Joint Typhoon Warning Center. 2008-03-31. Retrieved 2008-12-26.
  9. ^ a b Chris Landsea (1 June 2010). Subject: A15) How do tropical cyclones form ? National Hurricane Center. Retrieved on 2011-03-24.
  10. ^ a b Roger Graham Barry and Andrew Mark Carleton (2001). Synoptic and dynamic climatology. Psychology Press. pp. 520–521. ISBN 9780415031158. Retrieved 2011-03-06.
  11. ^ John Molinari and David Vollaro (2000). "Planetary- and Synoptic-Scale Influences on Eastern Pacific Tropical Cyclogenesis". Monthly Weather Review. 128 (9): 3296–307. Bibcode:2000MWRv..128.3296M. doi:10.1175/1520-0493(2000)128<3296:PASSIO>2.0.CO;2. Retrieved 2006-10-20. {{cite journal}}: Unknown parameter |month= ignored (help)
  12. ^ Roger Graham Barry and Richard J. Chorley (2003). Atmosphere, weather, and climate. Psychology Press. p. 271. ISBN 9780415271707. Retrieved 2011-03-06.
  13. ^ E. D. Maloney and D. L. Hartmann (2001). "The Madden–Julian Oscillation, Barotropic Dynamics, and North Pacific Tropical Cyclone Formation. Part I: Observations" (PDF). Journal of the Atmospheric Sciences. 58 (17): 2545–2558. Bibcode:2001JAtS...58.2545M. doi:10.1175/1520-0469(2001)058<2545:TMJOBD>2.0.CO;2. Retrieved 2008-06-24. {{cite journal}}: Unknown parameter |month= ignored (help)
  14. ^ Joint Typhoon Warning Center (2005). "2005 Annual Tropical Cyclone Report: Western Pacific" (PDF). United States Navy. Retrieved 2007-08-26.
  15. ^ a b James B. Elsner and Kam-Biu Liu (2003-10-08). "Examining the ENSO-Typhoon Hypothesis" (PDF). Climate Research. 25: 43. doi:10.3354/cr025043. Retrieved 2007-08-18.
  16. ^ Ricardo García-Herrera, Pedro Ribera, Emiliano Hernández and Luis Gimeno (2006). "Typhoons in the Philippine Islands, 1566-1900" (PDF). Journal of Geophysical Research. 112 (D6): 40. Bibcode:2007JGRD..11206108G. doi:10.1029/2006JD007370. Retrieved 2010-04-13.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Colleen A. Sexton (2006). Philippines in Pictures. Twenty-First Century Books. p. 16. ISBN 9780822526773. Retrieved 2008-11-01.
  18. ^ Edward B. Rodgers, Robert F. Adler, and Harold F. Pierce (October 2000). "Contribution of Tropical Cyclones to the North Pacific Climatological Rainfall as Observed from Satellites". Journal of Applied Meteorology. 39 (10). American Meteorological Society: 1662. Bibcode:2000JApMe..39.1658R. doi:10.1175/1520-0450(2000)039<1658:COTCTT>2.0.CO;2. Retrieved 2011-03-30.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  19. ^ Joint Typhoon Warning Center (2006). "3.3 JTWC Forecasting Philosophies" (PDF). United States Navy. Retrieved 2007-02-11.
  20. ^ a b M. C. Wu, W. L. Chang, and W. M. Leung (2003). "Impacts of El Nino-Southern Oscillation Events on Tropical Cyclone Landfalling Activity in the Western North Pacific". Journal of Climate. 17 (6): 1419–1428. Bibcode:2004JCli...17.1419W. doi:10.1175/1520-0442(2004)017<1419:IOENOE>2.0.CO;2. Retrieved 2007-02-11.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  21. ^ David J. Nemeth (1987). The architecture of ideology: neo-Confucian imprinting on Cheju Island, Korea. University of California Press. p. 51. ISBN 9780520097131. Retrieved 2011-03-06.
  22. ^ a b Japan Meteorological Agency (2001-05-25). "Annual Report on Activities of the RSMC Tokyo – Typhoon Center: 2000" (PDF). pp. iii, 11. Retrieved 2011-03-11.
  23. ^ Naval Meteorology and Oceanography Command (2011). "Products and Service Notice". United States Navy. Retrieved 2011-03-11.
  24. ^ Hong Kong Observatory (September 2010). "Tropical Cyclones in 2009" (PDF). pp. 18–19. Retrieved 2011-03-11.
  25. ^ "How typhoons are named". USA Today. 2007-11-01. Retrieved 2008-08-18.
  26. ^ Joint Typhoon Warning Center (2009). "Member Report Republic of the Philippines" (PDF). Philippine Atmospheric, Geophysical and Astronomical Services Administration. World Meteorological Organization. Retrieved 2010-04-14.
  27. ^ Joint Typhoon Warning Center (1959). "1958". United States Navy. {{cite web}}: Missing or empty |url= (help)
  28. ^ Erik Slavin (2005-05-30). "Preparation critical for Japan's coming typhoon season". Stars and Stripes. Retrieved 2011-03-06.
  29. ^ Kam-Biu Liu, Caiming Shen, and Kin-Sheun Louie (2001). "A 1,000-Year History of Typhoon Landfalls in Guangdong, Southern China, Reconstructed from Chinese Historical Documentary Records". Annals of the Association of American Geographers. 91 (3): 453–464. doi:10.1111/0004-5608.00253. ISSN 0004-5608.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  30. ^ George M. Dunnavan, John W. Diercks (1980). "An Analysis of Super Typhoon Tip (October 1979)". Monthly Weather Review. 108 (11). American Meteorological Society: 1915–1923. Bibcode:1980MWRv..108.1915D. doi:10.1175/1520-0493(1980)108<1915:AAOSTT>2.0.CO;2. ISSN 1520-0493. Retrieved 2011-03-31.
  31. ^ Anderson-Berry, Linda J. (2008-02-26). "Fifth International Workshop on Tropycal Cyclones: Topic 5.1: Societal Impacts of Tropical Cyclones". World Meteorological Organization. National Oceanic and Atmospheric Administration. Retrieved 2011-03-31. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  32. ^ Arizona State University (2009-08-12). "Taiwan Rainfall Record Investigation". Retrieved 2011-03-06.
  33. ^ "Record rains in south". The China Post. 2009-08-09. Retrieved 2009-08-09.

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