*******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 MAY 14 2020 5:35 PM EDT...
Early stages of a surface cyclone developing along a stalled front in the Florida straits already beginning...as this system heads northeast across the western Bahamas and into the western Atlantic it is expected to become a subtropical or tropical storm. Therefore temporarily continuing birdseye view posts before the official start of the Atlantic Hurricane Season on June 1st. See area of interest #1 below for details on this developing situation. Elsewhere...longer-range model runs now suggest less interaction between area of interest #1 and a highly amplified upper trough expected to be over the Great Lakes region in 4 days. This means this feature is likely to stay further west...over the eastern United States...instead of over the western Atlantic waters...reducing the chance that another subtropical system would develop immediately in the wake of area of interest #1. AREA OF INTEREST #1...A shortwave upper trough that was over the south-central United States has shifted southeastward into the Gulf of Mexico. The upper trough is beginning to amplify as adjacent warm upper ridging to the north is already beginning to amplify in warm southerly flow on the west side of a surface ridge moving into the western Atlantic. To the south of this surface ridge is a stalled surface front that was driven into the Florida straits and western Atlantic by a fairly large frontal cyclone that previously delivered unseasonably cold air across eastern North America. With its increasing eastern upper divergence...the amplifying shortwave upper trough in the Gulf of Mexico is already beginning to produce organizing shower and thunderstorms squalls with rotation along the stalled front. And combined with the fact that all computer models agree that a surface cyclone will soon emerge within this disturbance and track northeast along warm Gulf Stream waters in the western Atlantic in the coming days...it appears almost certain that a subtropical or tropical storm will form...therefore I have begun a subtropical/tropical cyclone formation forecast as outlined below. Warm air advection ahead of a pair of frontal lows to slide across the Great Lakes region of North America will continue to amplify upper ridging to the north and west...which will in turn amplify the shortwave upper trough further. The resulting surface cyclone will intensify in the increasing eastern divergence zone of the amplifying upper trough...and the more amplified nature of the shortwave shown in the latest model runs suggests less wind shear than I previously thought. Combined with the warm Gulf stream waters for thunderstorm activity...the surface cyclone is likely to be an intensifying subtropical storm in its early phases. At 72 to 96 hours...the latest modeling has become interesting...showing the cool shortwave upper trough dissipating due to strong warm air advection ahead of what is expected to be a robust second Great Lakes frontal low. This could allow for a fully tropical transition where the storm intensifies further due to low shear and upper outflow of overhead upper ridging...with the warm Gulf stream waters helping the thunderstorms and the latent heat release of the thunderstorms re-enforcing the upper ridging. However I shy just below hurricane strength in my forecast as the Gulf stream water temps at the 72 and 96 hour forecast points is only running 26 deg C...remember it is not hurricane season just yet. During the first 96 hours...this system is expected to track more north and less east across the western Bahamas and close to the United States east coast as the surface ridge currently moving into the western Atlantic blocks progress out to sea. In fact this system has potential to clip the Outer Banks of North Carolina...therefore interests here should watch the progress of this system. By the end of the 120-hour forecast period...an upper trough is currently expected to eject southeastward from the current energy over western Canada and arrive into southeastern Canada...with divergence out ahead of this upper trough creating a weakness in the western Atlantic surface ridge that is expected at this time to draw this system eastward away from the United States east coast. However convergence on the back side of the upper trough will create another surface ridge to the north...which combined with the western Atlantic surface ridge will make the weakness fairly narrow...therefore the eastward turn maybe slow and erratic late in the forecast. Upper westerly winds ahead of the upper trough...which will also try to drag this system east...will likely shear this system since the upper westerly wind speed will be faster than the east track of the system...therefore I show weakening at the end of the forecast period. I still expect a tropical system even late in the forecast period as the forecast track keeps this system perfectly following the warm Gulf stream waters. ******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast*********** 0 Hr Position (1800Z May 14)...Stalled front with rotation in the Florida straits in the vicinity of 23.5N-81.5W IOH 24 Hr Forecast (1800Z May 15)...Surface low developing into a subtropical depression centered between Florida...Grand Bahama Island...and Andros Island at 25.5N-79.5W IOH 48 Hr Forecast (1800Z May 16)...50 mph maximum sustained wind subtropical storm centered north of the northwest Bahamas and east of Florida at 28.5N-77.5W IOH 72 Hr Forecast (1800Z May 17)...65 mph maximum sustained wind tropical storm centered offshore of the southeastern United States at 31N-77.5W IOH 96 Hr Forecast (1800Z May 18)...70 mph maximum sustained wind tropical storm centered just east of Cape Hatteras North Carolina at 35N-75W IOH 120 Hr Forecast (1800Z May 19)...60 mph maximum sustained wind sheared tropical storm centered at 36.5N-71W