*******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 AUGUST 11 2020 10:05 AM EDT...
See area of interest section below for the central Atlantic tropical wave of low pressure being monitored for development.
Elsewhere...mutliple models continue to suggested the cold front currently over the central United States will become stretched southwest-to-northeast across the norhwestern Atlantic in about 4 days while its supporting upper vortex likewise becomes streteched by a warm upper ridge to build over Canada...with the front possibly becoming a focal point for tropical or subtropical cyclone formation. One possibility is the tail end of the front becomes embedded below upper ridging associated with warm air ahead of the front...with upper outflow and low shear beneath the ridging triggering tropical cyclone formation offshore of North Carolina or north of Bermuda next week. Another possiblity is the streteched upper vortex becomes re-concentrated south of Newfoundland and triggers a vigorous frontal cyclone along the north edge of the warm Gulf stream waters next week...in which case the frontal cyclone could acquire tropical characteristics and transition to a subtropical cyclone. Not declaring an area of interest out of this frontal zone at this time as the models solutions continue to vary without consensus at the present time.
AREA OF INTEREST #1...The tropical wave of low pressure moving into the central tropical Atlantic from the eastern Atlantic has overnight become much better organized while firing a persisting circular thunderstorm mass. However this system appears to be having some struggle while the center of circulation is on the southeast edge of the thunderstorm mass rather than directly under it...perhaps a sign of some easterly wind shear being generated by the strength of the tropical upper ridge in the region. Regardless...there appears to be enough organization to declare a tropical depression...therefore I have begun a tropical cyclone formation forecast for this system as outlined below. The intensity forecast is challenging as this system will slip by the unfavorable upper vorticity looming just to the north...thus remaining tucked beneath a cell of supporting tropical upper ridging on its journey toward the Lesser Antilles...and yet with the exception of the GFS none of the models strengthen this system. Perhaps this is an indication that dry saharan air may inhibit strengthening...so for now I forecast this system to become and then remain a steady-state weak tropical storm. The bullish GFS indicates rapid weakening by 96 to 120 hours...and a look at its forecast upper-level winds shows remnants of the current western Atlatnic upper trough lingering and potentially shearing this system. Thus I indicate weakening to a tropical depression at 120 hours.
Regarding the track forecast...I have nudged the track points northward due to the current position of this system...but I am not as far north as the model consensus. One reason is that this system through 96 hours looks to be well embedded beneath a cell of tropical upper ridging such that even if this system became strong/tall enough to be steered by upper winds...I don't see a mechanism to pull the system north. Even if I assume the models are picking up on some upper-level steering generated by the leftovers of the current western Atlantic upper trough...it still doesn't make sense as the model consensus is for a weaker/shallower system less likely to be steered by upper winds. I do agree with a more north angle in track by 120 hours however as the current frontal zone over the central United States will be eroding the current western Atlantic surface ridge by that timeframe.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Aug 11)...Tropical low pressure centered at 11.5N-38W
IOH 24 Hr Forecast (1200Z Aug 12)...40 mph maximum sustained wind tropical storm centered at 12N-43W
IOH 48 Hr Forecasat (1200Z Aug 13)...40 mph maximum sustained wind tropical storm centered at 12.5N-48W
IOH 72 Hr Forecast (1200Z Aug 14)...40 mph maximum sustained wind tropical storm centered at 13N-53W
IOH 96 Hr Forecast (1200Z Aug 15)...40 mph maximum sustained wind tropical storm centered just east of the Lesser Antilles at 13.5N-58W
IOH 120 Hr Forecast (1200Z Aug 16)...35 mph maximum sustained wind tropical depression centered in the eastern Caribbean Sea at 15N-63W
...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...located just northeast of the Lesser Antilles at 19.5N-59.5W in 120 hours...no strengthening shown. Elsewhere...possible subtropical cyclone formation shown in the northwest Atlantic near 40N-60W in 138 to 150 hours.
0000Z ECMWF Model Run...For area of interest #1...located just north of the Lesser Antilles near 20N-60.5W in 120 hours...no strengthening shown. Elsewhere...current central United States surface front becomes stretched across the northwestern Atlantic and North Carolina by 96 hours...by 120 hours two elongated low pressure systems form along the front (probably non-tropical and frontal in nature)...one east of North Carolina...the second south of Newfoundland.
0600Z GFS Model Run...For area of interest #1...strengthens as a compact tropical cyclone in 48 hours while passing 12.5N-47.5W...weakens while located just east of the northern Lesser Antilles at 17.5N-59.5W in 96 hours...opens into a tropical wave over the Virgin Islands by 120 hours. Elsewhere...current central United States surface front becomes stretched across the northwestern Atlantic and North Carolina by 96 hours...possible subtropical cyclone formation along east end of the front in the open central Atlantic near 35N-45W in 174 hours.
0600Z NAVGEM Model Run...For area of interest #1...weakens to a tropical wave along 52.5W longitude in 84 hours. Elsewhere...currently inactive tropical wave at 55W longitude shown to develop into a tropical cyclone just east of Nicaragua with the support of the Caribbean upper ridge cell in 138 hours. Current central United States surface front becomes stretched across the northwestern Atlantic and North Carolina by 96 hours...possible subtropical cyclone formation shown in the northwest Atlantic near 41N-59W in 168 hours.
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