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A post-tropical cyclone is a former tropical cyclone.〔http://www.nhc.noaa.gov/aboutgloss.shtml#p〕 Two classes of post-tropical cyclones are: * Extratropical cyclone, which is frontal, sometimes still retains winds of hurricane or tropical storm force.〔http://www.nhc.noaa.gov/aboutgloss.shtml#EXTRA〕 * Remnant low, which is non-frontal, has maximum sustained winds of less than 34 knots.〔http://www.nhc.noaa.gov/aboutgloss.shtml#REM〕 Not all systems fall into the above two classes. According to the guideline, a system without frontal characteristics but with maximum winds above 34 knots may not be designated as a remnant low. It should be merely described as post-tropical.〔http://www.nws.noaa.gov/om/notification/scn10-06trop_cyclone_terms.txt〕 A few examples falling into this gray area are listed below. *Eugene (2011)〔http://www.nhc.noaa.gov/archive/2011/ep05/ep052011.discus.026.shtml〕 *Michael (2012)〔http://www.nhc.noaa.gov/archive/2012/al13/al132012.discus.035.shtml?〕 *Nadine (2012)〔http://www.nhc.noaa.gov/archive/2012/al14/al142012.discus.043.shtml〕 *Humberto (2013) *Celia (2010)〔http://www.nhc.noaa.gov/archive/2013/al09/al092013.discus.024.shtml?〕 However, there has been an occasion that the United States National Hurricane Center violated the definition and designated Calvin (2011) as a 35-knot remnant low.〔http://www.nhc.noaa.gov/data/tcr/EP032011_Calvin.pdf〕 Also, if a tropical cyclone degenerates into a tropical wave or trough, then it does not qualify as a post-tropical cyclone. It would be referred as the "remnants of (tropical cyclone name)". In the South-West Indian Ocean, Météo-France classifies a tropical system as a “post-tropical depression” when it has begun an extratropical transition. Once it finishes the process, it will be classified as an extratropical depression. ==Origin== The terminology was initiated by Canadian Hurricane Centre in 1998 during Tropical Storm Bonnie.〔http://www.ec.gc.ca/ouragans-hurricanes/default.asp?lang=En&n=5375B60F-1〕 In 2008, the National Hurricane Center used this term for Tropical Storm Laura to address the limitation of the two classes (extratropical/remnant low) mentioned above.〔http://www.nhc.noaa.gov/archive/2008/al12/al122008.discus.010.shtml〕 The term was later adopted by the National Weather Service on May 15, 2010.〔http://www.nws.noaa.gov/om/notification/scn10-06trop_cyclone_terms.txt〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Post-tropical cyclone」の詳細全文を読む スポンサード リンク
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