*******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.**********
...MONDAY DECEMBER 23 2019 5:10 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 strengthening surface frontal low from the Gulf of Mexico has moved mostly over the southeastern United States while remaining supported by the increasing upper divergence on the east side of an upper trough which has recently amplified into an upper vortex due to adjacent amplification of warm upper ridging over the central United States (induced by warm air advection ahead of a strong frontal system sliding into western North America). I would describe this surface frontal low as a complex system with multiple centers...as earlier today the NHC TAFB surface analysis had the surface center analyzed over southern Georgia while satellite animation showed a well-defined swirl lingering further southwest in the northeastern Gulf of Mexico. The swirl was not the upper vortex as that feature is currently inland over southern Alabama. CIMSS 850 mb vorticity (http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=) suggested this swirl was mid-level while showing strong vorticity over the northeastern Gulf...but also CIMSS shows vorticity over southern Georgia. Most recently as of 1800Z...the NHC TAFB surface analysis now suggested the northeastern Gulf swirl...which is now about to make landfall in northern Florida...is the dominant surface center. Given that the dominant surface circulation remains further to the southwest...I have adjusted my updated forecast positions in the outlook below further southwest. The adjustment however is only slight as the supporting upper vortex of this storm system is still expected to quickly eject east-southeast into the western Atlantic by 24+ hours due to the building warm deep-layered ridging...which should bring an end to the heavy rain and gusty winds over the southeastern United States as upper-level convergence and resultant sinking dry air on the west side of the departing upper vortex and east side of the deep-layered ridge dominates over land...with the storm remaining in progress offshore in the eastern divergence zone of the upper vortex. Regarding the potential for this system to acquire tropical characteristics...it appears the surface center in the northeastern Gulf of Mexico will remain the dominant while the storm system moves east-southeast into the western Atlantic...but this center so far lacks showers and thunderstorms as water vapor satellite shows the aforementioned dry sinking air has wrapped into this center thus far. Thus I have lowered my odds of subtropical cyclone formation...but have not made them 0% as I am still waiting to see if the cold temperatures of the upper vortex and 24 deg C western Atlantic waters allows this center to develop thunderstorms in the next day or so. By 72 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 24)...0% chance of subtropical cyclone formation (just offshore of the southeastern United States coast near 30N-79.5W)
IOH 48 Hr Outlook (1200Z Dec 25)...10% chance of subtropical cyclone formation (western Atlantic near 28N-70.5W)
IOH 72 Hr Outlook (1200Z Dec 26)...0% chance of subtropical cyclone formation (western Atlantic near 25N-62W)