Editing Subtropical cyclone (section)

==Formation==
[[File:Maystormvapor.gif|thumb|left|A water vapor loop showing the formation of [[Subtropical Storm Andrea (2007)|Subtropical Storm Andrea]] in May 2007]]
Subtropical cyclones can form in a wide band of [[latitude]], mainly south of the 50th parallel in the [[northern hemisphere]], and north of the 50th parallel in the [[southern hemisphere]].<ref name="CLfaq">[[Chris Landsea]]. [http://www.aoml.noaa.gov/hrd/tcfaq/A6.html Subject: A6) What is a sub-tropical cyclone?] {{Webarchive|url=https://web.archive.org/web/20160603060427/http://www.aoml.noaa.gov/hrd/tcfaq/A6.html |date=2016-06-03 }} [[National Hurricane Center]]. Retrieved on 2008-06-14.</ref> Due to the increased frequency of cyclones which cut off from the main belt of the westerlies during the summer and fall, subtropical cyclones are significantly more frequent across the north Atlantic than the northwestern [[Pacific Ocean]].<ref>Mark A. Lander (2004). [http://ams.confex.com/ams/pdfpapers/75346.pdf 7A.5 Monsoon Depressions, Monsoon Gyres, Midget Tropical Cyclones, TUTT Cells, and High Intensity After Recurvature: Lessons Learned From Use of Dvorak's Techniques in the World's Most Prolific Tropical-Cyclone Basin.] {{Webarchive|url=https://web.archive.org/web/20090319013642/http://ams.confex.com/ams/pdfpapers/75346.pdf |date=2009-03-19 }} [[American Meteorological Society]]. Retrieved on 2009-02-28.</ref> In the eastern half of the north Pacific Ocean and north Indian Ocean, the older subtropical cyclone definition term is still used, which requires a weak circulation forming underneath a [[Upper tropospheric cyclonic vortex|mid to upper-tropospheric low]] which has cut off from the main belt of the westerlies during the cold season ([[winter]]), similar to the north [[Atlantic Ocean|Atlantic]] and southwest [[Indian Ocean]]. In the case of the north Indian Ocean, the formation of this type of vortex leads to the onset of [[monsoon]] rains during the [[wet season]].<ref name="Hast">S. Hastenrath (1991). [https://books.google.com/books?id=_UwvYopNedMC&dq=subtropical+cyclones+indian+ocean&pg=PA244 Climate Dynamics of the Tropics.] {{Webarchive|url=https://web.archive.org/web/20240128104144/https://books.google.com/books?id=_UwvYopNedMC&dq=subtropical+cyclones+indian+ocean&pg=PA244 |date=2024-01-28 }} Springer, pp 244. {{ISBN|978-0-7923-1346-5}}. Retrieved on 2009-02-29.</ref> In the [[southern hemisphere]], subtropical cyclones are regularly observed across southern portions of the [[Mozambique Channel]].<ref name="WMO2006" />

Most subtropical cyclones form when a deep [[cold-core low|cold-core]] [[extratropical cyclone]] drops down into the subtropics. The system becomes blocked by a high latitude ridge, and eventually sheds its frontal boundaries as its source of cool and dry air from the high latitudes diverts away from the system, and warms the central circulation, allowing further transition. Temperature differences between the 500&nbsp;hPa pressure level and the sea surface temperatures initially exceed the dry adiabatic [[lapse rate]], which causes an initial round of [[thunderstorms]] to form at a distance east of the center. Due to the initial cold temperatures aloft, sea surface temperatures usually need to reach at least {{convert|20|C|F}} for this initial round of thunderstorms. The initial thunderstorm activity humidifies the environment around the low pressure system, which destabilizes the atmosphere by reducing the [[lapse rate]] needed for convection. When the next shortwave or upper-level jet streak (wind maximum within the jet stream) moves nearby, the convection reignites closer to the center, which warms the core and develops the system into a true subtropical cyclone.<ref>{{Cite web |title=What Is a Subtropical Storm and How Is It Different From a Tropical Storm? {{!}} The Weather Channel - Articles from The Weather Channel {{!}} weather.com |url=https://weather.com/storms/hurricane/news/2020-11-04-what-is-a-subtropical-storm |access-date=2022-04-18 |website=The Weather Channel |language=en-US |archive-date=2022-06-02 |archive-url=https://web.archive.org/web/20220602223021/https://weather.com/storms/hurricane/news/2020-11-04-what-is-a-subtropical-storm |url-status=live }}</ref> The average sea surface temperature that helps lead to subtropical cyclogenesis is {{convert|24|C|F}}.<ref name="NAtlSTClimo"/><ref name="HistSubTropCyclones"/> If the thunderstorm activity becomes deep and persistent, allowing its initial low level warm core to deepen, extension to [[tropical cyclogenesis]] is possible.<ref name = "CLfaq"/> The locus of formation for north Atlantic subtropical cyclones is out in the open ocean; the island of Bermuda is regularly impacted by these systems.<ref name=" BermudaSTs">{{cite journal
  | title = Bermuda subtropical storms
  |author1=Mark P. Guishard |author2=Elizabeth A. Nelson |author3=Jenni L. Evans |author4=Robert E. Hart |author5=Dermott G. O’Connell | journal = Meteorology and Atmospheric Physics
  |volume=97 |issue=1–4 | date = August 2007
  | pages = 239–253
  | doi = 10.1007/s00703-006-0255-y
  |bibcode = 2007MAP....97..239G |s2cid=120260805 }}</ref>

The south Atlantic environment for formation of subtropical cyclones has both stronger vertical [[wind shear]] and lower [[sea surface temperature]]s, yet subtropical cyclogenesis is regularly observed in the open ocean in the south Atlantic. A second mechanism for formation has been diagnosed for south Atlantic subtropical cyclones: lee cyclogenesis in the region of the Brazil Current.<ref name="SAtlSTs"/>

Subtropical cyclone formation is extremely rare in the far southeastern Pacific Ocean, due to the cold sea-surface temperatures generated by the [[Humboldt Current]] and unfavorable [[wind shear]]. In late April 2015, [[Subtropical Cyclone Katie|a rare subtropical cyclone]] was identified to have formed in this region. This system was unofficially dubbed ''Katie'' by researchers.<ref name="[[Subtropical Cyclone Katie|Katie]]">{{cite web|author=Diamond, Howard J|work=Climate Program Office|publisher=National Oceanic and Atmospheric Administration|date=August 25, 2015|access-date=October 16, 2017|title=Review of the 2014/15 Tropical Cyclone Season in the Southwest Pacific Ocean Basin|url=http://cpo.noaa.gov/News/News-Article/ArtMID/6226/ArticleID/476/Review-of-the-201415-Tropical-Cyclone-Season-in-the-Southwest-Pacific-Ocean-Basin|archive-date=February 9, 2022|archive-url=https://web.archive.org/web/20220209013837/https://cpo.noaa.gov/News/News-Article/ArtMID/6226/ArticleID/476/Review-of-the-201415-Tropical-Cyclone-Season-in-the-Southwest-Pacific-Ocean-Basin|url-status=live}}</ref> [[Subtropical Cyclone Lexi|Another subtropical cyclone]] was identified at 77.8 degrees longitude in May 2018, just off the coast of Chile.<ref name="forms off the Chilean coast">{{Cite news|url=https://weather.com/storms/hurricane/news/2018-05-08-subtropical-cyclone-chile|title=Extremely Rare Southeast Pacific Subtropical Cyclone Forms Off the Chilean Coast|author=Jonathan Belles|work=The Weather Channel|date=May 9, 2018|access-date=May 10, 2018|archive-date=June 4, 2022|archive-url=https://web.archive.org/web/20220604001602/https://weather.com/storms/hurricane/news/2018-05-08-subtropical-cyclone-chile|url-status=live}}</ref> This system was unofficially named ''Lexi'' by researchers.<ref name="Lexi track">{{cite web|url=http://www.australiasevereweather.com/cyclones/2018/trak1805.htm|title=Monthly Global Tropical Cyclone Tracks - May 2018|author=Steve Young|publisher=Australia Severe Weather|date=5 July 2018|access-date=3 September 2018|archive-date=4 September 2018|archive-url=https://web.archive.org/web/20180904052433/http://www.australiasevereweather.com/cyclones/2018/trak1805.htm|url-status=live}}</ref> A subtropical cyclone was spotted just off the Chilean coast in January 2022.<ref>{{Cite web|url=https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=fxsa21&version=2&fmt=reg|title=South American Forecast Discussion|date=12 January 2022|access-date=15 January 2022|website=[[Weather Prediction Center]]|archive-url=https://archive.today/20220115193506/https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=fxsa21&version=2&fmt=reg|archive-date=15 January 2022|url-status=bot: unknown}}</ref><ref>{{Cite web|url=https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=fxsa21|title=South American Forecast Discussion|date=13 January 2022|access-date=15 January 2022|website=[[Weather Prediction Center]]|archive-url=https://archive.today/20220115193252/https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=fxsa21|archive-date=15 January 2022|url-status=bot: unknown}}</ref>

===Transition from extratropical===
By gaining tropical characteristics, an extratropical low may transit into a subtropical depression or storm. A subtropical depression/storm may further gain tropical characteristics to become a pure tropical depression or storm, which may eventually develop into a hurricane, and there are at least ten cases of tropical cyclones transforming into a subtropical cyclone ([[Tropical Storm Gilda (1973)|Tropical Storm Gilda]] in 1973, [[Subtropical Storm Four (1974)|Subtropical Storm Four]] in 1974, [[1981 Atlantic hurricane season#Tropical Storm Jose|Tropical Storm Jose]] in 1981, [[Hurricane Klaus (1984)|Hurricane Klaus]] in 1984, [[Tropical Storm Allison]] in 2001, [[Tropical Storm Lee (2011)|Tropical Storm Lee]] in 2011, [[2013 Atlantic hurricane season#Hurricane Humberto|Hurricane Humberto]] in 2013, [[2016 Atlantic hurricane season#Tropical Storm Ian|Tropical Storm Ian]] in 2016, [[Typhoon Jelawat (2018)|Typhoon Jelawat]] in 2018, and [[Typhoon Surigae]] in 2021). There have also been three recorded cases of a storm transitioning from tropical to extratropical back to a subtropical cyclone; as seen with the [[1970 Caribbean–Azores hurricane|Caribbean–Azores hurricane]] in 1970, [[1980 Atlantic hurricane season#Hurricane Georges|Hurricane Georges]] in 1980, and [[Hurricane Beryl (2018)|Hurricane Beryl]] in 2018. Generally, a tropical storm or tropical depression is not called subtropical while it is becoming extratropical and vice versa, after hitting either land or colder waters. This transition normally requires significant instability through the atmosphere, with temperature differences between the underlying ocean and the mid-levels of the [[troposphere]] requiring over 38&nbsp;°C, or 68&nbsp;°F, of contrast in this roughly {{convert|5900|m|ft|sp=us}} layer of the lower atmosphere. The [[mode (statistics)|mode]] of the sea surface temperatures that subtropical cyclones form over is {{convert|23|C|F}}.<ref name="HistSubTropCyclones">{{cite web| title = A Fifty-year History of Subtropical Cyclones| author = David Mark Roth| publisher = Hydrometeorological Prediction Center| date = 2002-02-15| url = http://www.wpc.ncep.noaa.gov/research/roth/Subpreprint.pdf| access-date = 2006-10-04| archive-date = 2021-04-17| archive-url = https://web.archive.org/web/20210417020816/https://www.wpc.ncep.noaa.gov/research/roth/Subpreprint.pdf| url-status = live}}</ref> Transition from subtropical cyclones into fully tropical cyclones occurs only in very rare cases over the south Atlantic Ocean, such as [[Hurricane Catarina]] in 2004.<ref name="SAtlSTs"/>