Post-tropical cyclone
A post-tropical cyclone is a former tropical cyclone.[1] Two classes of post-tropical cyclones are:
- Extratropical cyclone, which is frontal, sometimes still retains winds of hurricane or tropical storm force.[2]
- Remnant low, which is non-frontal, has maximum sustained winds of less than 34 knots.[3]
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.[4] A few examples falling into this gray area are listed below.
- Celia (2010)[5]
- Eugene (2011)[6]
- Michael (2012)[7]
- Nadine (2012)[8]
- Sandy (2012)
- Humberto (2013)
- Joaquin (2015)[9]
- Hermine (2016)
- Matthew (2016)[10]
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.[11]
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.
Formation
A post-tropical cyclone is formed when the typical characteristics of a tropical cyclone are replaced with those of extratropical cyclones, otherwise known as extratropical transition.[12] After the initial formation, a post-tropical cyclone has the potential to gain strength and intensity by forming an extratropical storm.[12] If a post-tropical cyclone does become an extratropical storm, it will eventually decay through the process of occlusion.[13]
Impacts
The re-intensification of a post-tropical cyclone can cause dangerous conditions in North Atlantic shipping routes with high seas and winds comparable to those of hurricanes.[12]
Origin
The terminology was initiated by Canadian Hurricane Centre in 1998 during Tropical Storm Bonnie.[14] 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.[15] The term was later adopted by the National Weather Service on May 15, 2010.[4]
Synonym
The Bureau of Meteorology in Australia refers a former tropical cyclone as an "ex-tropical cyclone". An example is ex-tropical cyclone Oswald.
References
- ↑ "Glossary of NHC Terms".
- ↑ "Glossary of NHC Terms".
- ↑ "Glossary of NHC Terms".
- 1 2 http://www.nws.noaa.gov/om/notification/scn10-06trop_cyclone_terms.txt
- ↑ "Post-Tropical Cyclone HUMBERTO".
- ↑ "Post-Tropical Cyclone EUGENE".
- ↑ "Post-Tropical Cyclone MICHAEL".
- ↑ "Post-Tropical Cyclone NADINE".
- ↑ "Post-Tropical Cyclone JOAQUIN".
- ↑ "Post-Tropical Cyclone MATTHEW Public Advisory". www.nhc.noaa.gov. Retrieved 2016-10-09.
- ↑ http://www.nhc.noaa.gov/data/tcr/EP032011_Calvin.pdf
- 1 2 3 Pelissero, Jonathon; Chiao, Sen (July 5, 2013). "The influences of post-tropical reintensification and dissipation on North Atlantic shipping routes". Meteorological Applications. Royal Meteorological Society. 21 (3).
- ↑ "Extratropical Cyclone". britannica.com. Encyclopaedia Britannica. Retrieved October 27, 2016.
- ↑ http://www.ec.gc.ca/ouragans-hurricanes/default.asp?lang=En&n=5375B60F-1
- ↑ "Tropical Storm LAURA".