*******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.**********
...SUNDAY DECEMBER 22 2019 3:53 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 trough of low pressure in the Gulf of Mexico has evolved into a frontal low making landfall into the southeastern United States...and remains supported by widespread upper divergence ahead of an upper trough moving into the eastern United States. Over the next 24 hours...warm deep-layered ridging over the central United States will continue to amplify in warm air advection ahead of a strong frontal system moving into western North America. In turn...this will cause the adjacent eastern United States upper trough to amplify into an upper vortex...with strengthening divergence on the east side of the upper vortex to intensify the surface frontal low as it moves across the southeastern United States. The strengthening surface frontal low will have an increasingly tighter pressure gradient with respect to a surface ridge to the northeast supported by convergence on the back side of broad northwestern Atlantic upper troughing...so although the surface low will not be acquiring tropical characteristics during the next 24 hours heavy rainfall...coastal sea swells...and gusty winds are expected over parts of the southeastern United States. Based on the larger shield of heavy rain on doppler radar...I have expanded the areas impacted in the special messages section on the home page of this site. In 48 to 72 hours...the upper vortex and surface frontal low is expected to quickly shift east-southeast across the western Atlantic between the Bahamas and Bermuda due to the strength of the aforementioned warm deep-layered ridging over the United States. This is when I forecast some potential for this system to acquire some tropical characteristics with instability for thunderstorms possibly provided by 24 deg C waters and cold temperatures of the upper vortex. By 96 hours...the broad northwestern Atlantic upper troughing is forecast to amplify southward due to the strength of the 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%. For the first 48 hours...I have adjusted the forecast positions for this system westward due to the current position of the surface frontal low. In the next 24 hours the current more west center should lose its dominance as it whirls beneath the center of the forecast upper vortex where there will be a lack of upper divergence...with divergence on the east side of the upper vortex making a new center over southern Georgia. My forecast positions are the same at 72 and 96 hours as the 1200Z GFS shows the upper vortex ejecting quickly east-southeast into the western Atlantic...which makes me think the surface low will still end up further east and catch up to the previous forecast.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Dec 23)...0% chance of subtropical cyclone formation (southern Georgia near 31.5N-82.5W)
IOH 48 Hr Outlook (1200Z Dec 24)...10% chance of subtropical cyclone formation (offshore of the southeastern United States coast near 30.5N-79W)
IOH 72 Hr Outlook (1200Z Dec 25)...15% chance of subtropical cyclone formation (western Atlantic near 29N-70.5W)
IOH 96 Hr Outlook (1200Z Dec 26)...0% chance of subtropical cyclone formation (western Atlantic near 25.5N-61W)