*******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.**********
...MONDAY SEPTEMBER 28 2020 10:22 AM EDT...
The tail end of the cold front currently moving across the eastern United States will cross the Gulf of Mexico and enter the western Caribbean Sea over the next few days...computer models continue to suggest that upper-level winds over the western Caribbean will also become increasingly favorable for the tail end of the front to undergo tropical development and the National Hurricane Center has also marked the western Caribbean in their 5-day tropical weather outlook. Therefore I introduced the tail end of the frontal zone as an area of interest for tropical development...see area of interest #1 section below for details.
On Sunday morning the National Hurricane Center in their tropical weather outlook briefly mentioned the persistent remnant low pressure of Paulette which has been drifting west-northwestward back toward the Azores around a surface ridge in the northeastern Atlantic...as it once again produced some shower and thunderstorm flares near its center while in a low shear pattern beneath cut-off upper vorticity in the region. However the water temperatures in the region are too cool and the cut-off upper vorticity was too warm for this activity to persist such that this activity has long since dissipated...and now upper-level winds are hostile for the remnant low pressure to undergo any kind of tropical redevelopment as a north Atlantic upper trough has swept away the cut-off upper vorticity and exposed the remnant low pressure of Paulette to a long fetch of shearing upper westerly winds. The remnant low pressure should continue westward around the north Atlantic surface ridge and finally be defeated by a regime of upper-level convergence to occur on the east side of a warm upper ridge to amplify in the northwestern Alantic in the warm sector of the frontal system currently over the eastern United States.
Various long range runs of the NAVGEM and ECMWF over the last couple of days have suggested a tropical wave of low pressure to emerge from western Africa may develop in the eastern tropical Atlantic underneath a favorable upper ridge to persist over the region...therefore may have to watch this region as well in the coming days. And finally...recent runs of the GFS and NAVGEM have suggested the tropical wave of low pressure currently in the open Atlantic near 35W longitude may amplify (intensify) in a regime of split flow upper divergence upon entering the eastern or central Caribbean Sea in a few days. This upper air pattern will occur if the northwestern Atlantic shortwave upper trough dives southward toward the eastern Caribbean Sea due to the expansion of the northwestern Atlantic upper ridge to be induced by the warm sector of the current frontal system over the eastern US...with the split upper level flow occuring between the southwest side of the upper trough and southeast side of the Caribbean upper ridge to build over area of interest #1. The split flow upper divergence could result in the tropical wave intensifying into a possible eastern or central Caribbean Sea tropical cyclone to the east of area of interest #1 by next week.
AREA OF INTEREST #1...High-latitude upper trough energy has pivoted southeastward across central North America while pulled toward an upper vortex over central Canada...driving a surface cold front across the central and eastern United States...and the tail end of this cold front is expected to reach the western Caribbean Sea in 2 to 3 days. In 4 to 5 days...upper-level winds over the western Caribbean will become more conducive for tropical development as the central North America upper trough regime relaxes...allowing an upper ridge with low shear and upper outflow to expand in the trough regime's wake...therefore watching to see if the tail end of the front evolves into a tropical disturbance in the western Caribbean Sea. Various runs of the NAVGEM and now the GFS over the last couple of days have suggested tropical cyclone formation from this setup...and given the consistency in the models in the evolution of a more a favorable upper wind pattern setting up I am currently forecasting a 40% chance of tropical cyclone formation by day 5. Any tropical cyclone that does form here will likely move initially west around the south side of the strong surface ridge currently building over North America and supported by the western convergence zone of the developing central North America upper trough regime...with an increasing north bend in track toward the Gulf of Mexico with time possible should this system become a strong/tall enough tropical cyclone to be guided by upper southwesterly flow ahead of a shortwave upper trough to pivot southeastward around the west side of the central North America upper trough regime and toward the Gulf of Mexico and southeastern United States.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 29)...0% chance of tropical cyclone formation (central Gulf of Mexico near 26N-89W)
IOH 48 Hr Outlook (1200Z Sep 30)...0% chance of tropical cyclone formation (just offshore of northwestern Cuba near 23.5N-84W)
IOH 72 Hr Outlook (1200Z Oct 1)...0% chance of tropical cyclone formation (northwestern Caribbean Sea to the east of the Yucatan peninsula and south of western Cuba near 20N-85W)
IOH 96 Hr Outlook (1200Z Oct 2)...20% chance of tropical cyclone formation (northwestern Caribbean Sea to the east of the Yucatan peninsula and south of western Cuba near 20N-85W)
IOH 120 Hr Outlook (1200Z Oct 3)...40% chance of tropical cyclone formation (northeastern corner of the Yucatan peninsula near 21N-87W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...For area of interest #1...surface low consolidates north of Honduras and east of Belize at 126 hours.
0000Z ECMWF Model Run....For area of interest #1...surface trough consolidates in the western Caribbean Sea just to the west of the Cayman Islands by 120 hours. Elsewhere...tropical wave with organized low pressure spin emerges from western Africa in 144 hours...rapid tropical cyclone formation suggested just east-southeast of the Republic of Cabo Verde Islands in 168 hours.
0600Z GFS Model Run...For area of interest #1...surface low consolidates between the Cayman Islands and Honduras in 96 hours near 16.5N-84W...tropical cyclone formation suggested just east of the Yucatan peninsula in 120 hours...makes landfall over the northeastern Yucatan peninsula in 132 hours as a strenghtening tropical cyclone.
0600Z NAVGEM Model Run...For area of interest #1...no tropical cyclone formation shown. Elsewhere...tropical wave currently near 35W longitude becomes better defined in the eastern Caribbean Sea at 102 hours...develops into a tropical cyclone over the east coast of the Dominican Republic at 144 hours.