*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.********** ...TUESDAY MAY 12 2020 8:30 AM EDT...
Vigorous frontal cyclone with potential to acquire tropical characteristics expected to form southwest of Bermuda in 5 days. Therefore temporarily resuming birdseye view posts before the official start of the Atlantic Hurricane Season on June 1st. See area of interest section below for details. AREA OF INTEREST #1...A shortwave upper trough currently producing showers and thunderstorms over the south-central United States is expected to shift eastward into the western Atlantic over the next 5 days. As this occurs...a pair of frontal low pressure systems will slide across the Great Lakes region of North America...the first to be supported by an upper trough trailing from the current unseasonably cold upper vortex over eastern Canada...the second to be supported by energy currently just offshore of the northwestern US. It appears warm air advection (northward transport of warm air) ahead of both frontal low pressure systems will induce enough upper ridging over the northeastern US and northwestern Atlantic to cause the shortwave upper trough to amplify into a cut-off upper vortex as it moves into the western Atlantic. This is a classic pattern to support the formation of a surface frontal cyclone and possible acquisiton of tropical characteristics through thunderstorms caused by divergence on the east side of the cut-off upper vortex...and perhaps instability through cold enough upper air temperatures of the upper vortex. At 96 hours...despite being over 26+ deg C waters abundant for tropical development...the forecast surface frontal cyclone will only be in its formative stages as a surface trough without a closed circulation..therefore I still have 0% odds of development through that time. By 120 hours the rapdily forming frontal cyclone will likely shift quickly northeast toward cooler 22 deg C waters in the vicinity of 29N-70W...into the supportive eastern divergence zone of the forecast cut-off upper vortex. By that point it will require cold upper air temperatures for instability and thunderstorms...but since the shortwave upper trough expected to become a cut-off upper vortex is of southern origin it is not expected to be very cold...only forecast to measure 1220 dekameters on a 200 mb height map in this morning's 0600Z GFS model run (mag.ncep.noaa.gov). When studying some of the subtropical cyclone formations from October last year...200 mb heights over similar water temperatures were below 1200 dekameters. Therefore I have only low odds of subtropical cyclone formation...10%...by 120 hours. By that time upper divergence on the east side of the cut-off upper vortex is expected to become very high as the upper flow splits between mainstream mid-latitude westerlies and the flow around the vortex...so thunderstorm activity may be boosted enough by the divergence to help subtropical development despite the aforementioned thermal profile. On a final note...all major computer models (CMC...NAVGEM...GFS...ECMWF) are in very strong agreement on a western Atlantic frontal cyclone forming from a cut-off upper vortex by day 5...part of the reason why I've begun birdseye view posts on this situation from now. ******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook*********** IOH 24 Hr Outlook (0600Z May 13)...0% chance of subtropical cyclone formation (eastern Texas near 32N-97.5W) IOH 48 Hr Outlook (0600Z May 14)...0% chance of subtropical cyclone formation (eastern Texas near 32N-95W) IOH 72 Hr Outlook (0600Z May 15)...0% chance of subtropical cyclone formation (Florida...western Bahamas...and adjacent waters near 29N-80W) IOH 96 Hr Outlook (0600Z May 16)...0% chance of subtropical cyclone formation (just northeast of the central Bahamas near 25N-72.5W) IOH 120 Hr Outlook (0600Z May 17)...10% chance of subtropical cyclone formation (western Atlantic near 29N-70W)