*******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.**********
...THURSDAY NOVEMBER 19 2020 11:05 PM EDT...
See area of interest sections below for an update on the areas in the Atlantic being monitored for tropical cyclone formation.
AREA OF INTEREST #1...The surface trough of low pressure in the western Atlantic north of the eastern Caribbean Islands has merged with the surface cold front of the upper trough that recently exited North America at a location just east of the Bahamas...or near 22.5N-70W. The upper trough is leaving behind a cold core string of upper vorticity that will soon become an east-west oriented cut-off upper vortex in response to an adjacent amplified warm eastern US upper ridge to build ahead of another cold front that will pivot southeast across central Canada. As the upper vortex forms in the next 48 hours...upper divergence will increase and wind shear will reduce on the east side of the upper vortex...which could result in the formation of a tropical disturbance along the tail end of the current western Atlantic cold front currently east of the Bahamas. The forecast positions in the outlook below are adjusted eastward and are based on the location of the upper divergence maximum on the east side of the forecast upper vortex in the 1800Z GFS model run. By 72+ hours...the upper ridge over the eastern US will erode as the cold front and upper trough over from central Canada approaches...which will cause the upper vortex to de-amplify as it merges with incoming upper trough...resulting in an increase in wind shear. Thus by 96 hours I drop odds of development to 0%. I forecast a low 10% chance of tropical cyclone formation by 48 hours instead of 24 hours as it will take at least 24 hours for a tropical disturbance to organize in the eastern divergence zone of the forecast upper vortex...and keep the 10% odds through 72 hours as this is when the wind shear only begins to increase. The odds are kept low as their continues to be a lack of computer model support...with any of the models that show a closed surface circulation developing being too late in the window of time where shear increases...with absorption into the cold front arriving from central Canada not long after once the front moves into the Atlantic which would transition this system to non-tropical (see 1200Z ECMWF or CMC runs in the model summary below for examples).
*******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Nov 20)...0% chance of tropical cyclone formation (western Atlantic near 25N-64W)
IOH 48 Hr Outlook (1800Z Nov 21)...10% chance of tropical cyclone formation (western Atlantic near 27N-64W)
IOH 72 Hr Outlook (1800Z Nov 22)...10% chance of tropical cyclone formation (western Atlantic near 27N-64W)
IOH 96 Hr Outlook (1800Z Nov 23)...0% chance of tropical cyclone formation (south of Bermuda near 30N-64W)
AREA OF INTEREST #2...The tropical wave of low pressure currently moving westward through the Caribbean Sea has crossed 78W longitude as of 1800Z tonight...and is merging with a field low surface pressure supported by the outflow of a Caribbean upper ridge cell that remains stationary over the last several days. However their remains a lack of thunderstorms in the tropical wave such that tropical cyclone formation is no longer possible as the wave will soon make landfall in Nicaragua just after 24 hours. The tropical wave has been removed from the NHC tropical weather outlook tonight...and this is my final statement on this tropical wave on this blog.
*******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Nov 20)...0% chance of tropical cyclone formation (just offshore of southern Nicaragua near 12.5N-82W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z CMC Model Run... For area of interest #1...surface low consolidates just north of Bermuda at 126 hours....quickly transitions to a non-tropical low along an incoming front to the northwest in the long range. For area of interest #2...no tropical cyclone formation shown.
1200Z ECMWF Model Run...For area of interest #1...evolves into an elongated suface low pressure just northeast of the Bahamas at 96 hours...quickly transitions to a non-tropical low along an incoming front to the northwest by 120 hours. For area of interest #2...no tropical cyclone formation shown.