subtropical cyclone subtropical cyclone weather system characteristics tropical extratropical cyclone early 1950s unclear characterized tropical extratropical cyclones officially recognized national_hurricane_center subtropical cyclones began receive names official tropical cyclone lists north_atlantic south west indian_ocean basins definitions currently subtropical cyclones north atlantic southwest indian ocean require central convection fairly near center warming core mid levels eastern half northern pacific require mid cyclone cut main belt weak surface circulation subtropical cyclones broad wind patterns maximum sustained winds located farther center typical tropical cyclones weather fronts linked center form initially extratropical cyclones colder temperatures aloft normally found tropics sea surface temperatures required formation lower tropical cyclone threshold lying means subtropical cyclones likely form outside traditional bounds north_atlantic hurricane season subtropical cyclones observed form subtropical cyclones observed months history term 1950s 1960s term semi tropical quasi tropical known subtropical cyclones term subtropical cyclone merely referred cyclone located subtropical belt near north horse latitudes intense debate ensued late 1960s number hybrid cyclones formed national_hurricane_center nhc finally designated storms subtropical cyclones real time updated hurricane database include subtropical cyclones term began small subtropical cyclones formed features nhc began issuing public statements atlantic hurricane season employing classification noted controversial contemporary news reports dropped year later recent articles published year suggested considered 1970s appear published reports period making claim naming north_atlantic basin subtropical cyclones initially named nato alphabet list early mid-1970s intervening years subtropical storms named traditional list considered tropical real time separate numbering system different numbers given subtropical depressions subtropical storms public use nhc reference example hurricane karen initially known subtropical storm short nhc began giving numbers subtropical depressions names subtropical storms sequence tropical cyclones onwards subtropical depression known subtropical depression thirteen instead subtropical storm receive tropical shortly naming atlantic hurricane season subtropical storm tropical policy change subtropical storm atlantic hurricane season tropical named recognized post season analysis southern indian ocean subtropical cyclones named winds reach tropical storm gale force subtropical storms named formation subtropical cyclones form wide band latitude mainly south 50th parallel northern hemisphere increased frequency cyclones cut main belt summer fall subtropical cyclones significantly frequent north_atlantic northwestern pacific ocean eastern half north pacific ocean north indian ocean older subtropical cyclone definition term requires weak circulation forming underneath mid upper low cut main belt cold season winter case north indian ocean formation type vortex leads onset monsoon rains wet season southern hemisphere subtropical cyclones regularly observed southern portions subtropical cyclones form deep cold core extratropical cyclone drops system blocked high latitude ridge eventually sheds frontal boundaries source cool dry air high latitudes away system temperature differences hpa pressure level meters ground level sea surface temperatures initially exceed dry lapse rate causes initial round thunderstorms form distance east center initial cold temperatures aloft sea surface temperatures usually need reach initial round thunderstorms initial thunderstorm activity environment low atmosphere reducing lapse rate needed convection upper level jet streak wind maximum jet stream moves nearby convection closer center system develops true subtropical cyclone average sea surface temperature helps lead subtropical cyclogenesis thunderstorm activity deep persistent allowing initial low level warm core tropical cyclogenesis possible formation north_atlantic subtropical cyclones open ocean island bermuda regularly impacted systems environment formation subtropical cyclones stronger vertical wind shear lower sea surface temperatures subtropical cyclogenesis regularly observed open ocean second mechanism formation diagnosed subtropical cyclones lee cyclogenesis region transition extratropical gaining tropical characteristics extratropical low transit subtropical depression storm subtropical depression storm gain tropical characteristics pure tropical depression storm eventually develop hurricane cases tropical storms transforming subtropical storm tropical storm tropical storm lee generally tropical storm tropical depression called subtropical extratropical hitting land colder waters transition normally requires significant instability atmosphere temperature differences underlying ocean mid levels requiring contrast roughly meters layer lower atmosphere mode sea surface temperatures subtropical cyclones form transition subtropical cyclones tropical cyclones occurs rare cases hurricane characteristics storms maximum winds extending farther center purely tropical cyclone weather fronts linking directly center circulation maximum recorded wind speed subtropical storm knots mph minimum hurricane united_states subtropical cyclones similarly tropical cousins based maximum sustained surface winds winds knots mph called subtropical depressions speed referred subtropical storms subtropical cyclones likely tropical cyclones form outside region designated hurricane season north_atlantic examples include subtropical storm alex hurricane alex mid january atlantic hurricane season tropical storm late april hurricane season early tropical storm mid december atlantic hurricane season subtropical storm tropical storm late hurricane season depict cyclone phase depict subtropical cyclones shallow warm core systems similar tropical cyclones begun transition extratropical cyclone types upper level low common type subtropical storm upper level cold low circulation extending surface layer maximum sustained winds generally occurring radius kilometers center comparison tropical cyclones systems relatively broad zone maximum winds located farther center typically wind field distribution convection low second type subtropical cyclone low originating near zone horizontal wind shear known dying frontal zone radius maximum sustained winds generally kilometers entire circulation initially diameter kilometers generally short lived systems cold core warm core type subtropical cyclone referred storm storms lows deep cyclones form cool season central pacific ocean definition change term early 1970s makes systems complex lows extratropical cyclones complete weather fronts northeast pacific ocean consider subtropical cyclones long weak surface circulation present hawaiian term explains change wind direction easterly southerly type cyclone present australian australian east coast lows known locally east coast lows east coast cyclones extratropical cyclones intense systems characteristics subtropical cyclones develop south south australian coastline typically winter months year significant impact maritime lows explosive cyclogenesis seen average year storms cause significant wind flood damage occur australian east coast cyclones vary size approximately scale approximately storms affect south east coast confused australian region tropical cyclones typically affect northern half continent
Subtropical cyclone