*******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 DECEMBER 24 2019 3:21 PM EDT...
Temporarily resuming birdseye view posts on the Atlantic tropics due to the feature mentioned in area of interest section below.
AREA OF INTEREST #1...The broad surface frontal low that was over the northeastern Gulf of Mexico and southeastern United States yesterday has shifted eastward and is now located in the western Atlantic north of the western Bahamas and offshore of the southeastern United States. This system has had two pockets of low pressure dueling with each other...one that was over the northeastern Gulf and one that was over southern Georgia. It appears the eastern pocket is dominating while aligned with the eastern divergence zone of the parent upper vortex overhead...while the western pocket is weakening directly under the upper vortex center where there is a lack of divergence. Thus it appears to me this broad surface circulation is now centered further east...near 30N-77.5W...but is elongated east-to-west due to the presence of the western pocket. The latest ASCAT passes of surface winds seem to jive with this assessment. Thus I have adjusted my forecast positions in the outlook below to be further east. Regarding the potential for acquisiton of tropical characteristics...water vapor satellite shows that the more east location of this system is keeping it further away from the very dry sinking air to the west...currently over Florida...the eastern Gulf of Mexico...and western Cuba...caused by upper-level convergence on the west side of the upper vortex and east side of amplifying warm deep-layered ridging over the United States (the ridging is bolstered by warm southerly flow ahead of a western US frontal system). This has has allowed a curved band of showers and thunderstorms to fire just north of the new more eastern center...in part driven by the instability between the cold temperatures of the upper vortex and 23 to 24 deg C waters. However I have lowered peak odds of subtropical cyclone formation to only 5% as the elongated nature of the surface circulation may never allow this system to be considered a subtropical cyclone regardless of shower and thunderstorm activity...and as the National Hurricane Center is not mentioning this system in its tropical weather outlook. By 48 hours...broad northwestern Atlantic upper troughing is forecast to amplify southward due to the strength of the deep-layered ridging over the United States...which will allow it to absorb the upper vortex. This upper air pattern will result in increasingly unfavorable westerly wind shear across the western Atlantic as the upper vortex loses its defintion...and this is when I drop the odds of subtropical development down to 0%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Dec 25)...5% chance of subtropical cyclone formation (western Atlantic near 28N-70W)
IOH 48 Hr Outlook (1200Z Dec 26)...0% chance of subtropical cyclone formation (western Atlantic near 25N-62W)