MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #4
Updated: May 19
*******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.********** ...FRIDAY MAY 15 2020 11:56 PM EDT...
Surface low pressure system beginning to form in the waters of the Florida straits...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 have shifted further east with the position of a potent upper trough expected to arrive into the Great Lakes region of North America in 3 to 4 days. This positions the associated surface low pressure system to be further east along the United States east coast instead of inland...which only slightly increases the chances that yet another subtropical system could develop in the wake of area of interest #1. Need to see model runs show this system developing more offshore and come into better agreement before declaring it as another area of interest. AREA OF INTEREST #1...The shortwave upper trough in the Gulf of Mexico continues to shift ever so slightly east toward the Florida peninsula. This upper trough is continuing to amplify as adjacent warm upper ridging to the north also continues to amplify in warm southerly flow on the west side of a west Atlantic surface ridge and east side of a frontal low moving through the Great Lakes region of North America. The increasing upper divergence on the east side of the amplifying upper trough has produced a new surface low pressure centered in the Florida Straits as of 1200Z and 1800Z earlier today...which features shower and thunderstorm squalls extending well north and east of the center. An ASCAT-A descending pass confirmed the 1800Z NHC TAFB surface analysis center fix of 25N-80W...but also showed the circulation was not yet fully closed at the surface. The pattern of amplifying warm upper ridging to the north and west is expected to continue as another round of warm air advection occurs ahead of a second more vigrous frontal cyclone and upper trough to enter the Great Lakes region in 3 to 4 days. This will in turn amplify the upper trough currently in the Gulf of Mexico further. The surface low pressure center currently in the Florida Straits will intensify into a more mature cyclone in the increasing eastern divergence zone of the amplifying upper trough...and the more amplified nature of the upper trough means less wind shear with time. 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 48 to 72 hours...the latest modeling has become interesting...showing the cool Gulf of Mexico upper trough dissipating due to the aforementioned strong warm air advection ahead of the Great Lakes weather system to arrive in 3 to 4 days. 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 48 and 72 hour forecast points is only running 26 deg C...remember it is not hurricane season just yet. In fact...my intensity forecast is slightly lowered as the current surface low pressure system is not as well-developed as I previously though it would be by now...and infrared satellite imagery so far has shown the thunderstorm activity to be scattered/spotty instead of widespread. During the first 72 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 in 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 continue to watch the progress of this system. By 96 to 120 hours...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 has potential 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. The NAVGEM...CMC...and Euro models accelerate this system eastward through the weakness while the 1800Z GFS suggested the weakness would not be enough to pull this system out to sea...instead showing this system stall offshore of the northeastern United States coast and then get absorbed by the vigorous weather system from the Great Lakes. Given that three of the four models show an out to sea solution and have trended further east with the positioning of the Great Lakes system...which would tend to push this system away from the coast with its southeast quadrant...I continue to show an out to sea solution in the long range. Meanwhile in the short-term my forecast track is nudged south and west given the current position of the surface low with respect to my previous forecast. Upper westerly winds ahead of the upper trough expected over southeastern Canada in 96 to 120 hours will likely shear this system...so I show a slightly lower forecast intensity during this timeframe. 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 15)...New surface low pressure centered in the Florida Straits at 25N-80W IOH 24 Hr Forecast (1800Z May 16)...40 mph maximum sustained wind subtropical storm centered over the northwest Bahamas at 27N-78W IOH 48 Hr Forecast (1800Z May 17)...60 mph maximum sustained wind tropical storm centered offshore of the southeastern United States at 29.5N-78W IOH 72 Hr Forecast (1800Z May 18)...65 mph maximum sustained wind tropical storm centered just south of Cape Hatteras North Carolina at 34.5N-75.5W IOH 96 Hr Forecast (1800Z May 19)...50 mph maximum sustained wind sheared tropical storm centered at 36.5N-70W IOH 120 Hr Forecast (1800Z May 20)...50 mph maximum sustained wind sheared tropical storm centered at 36.5N-65W