*******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 17 2024 1:30 PM EDT...
Resuming daily posts on the Atlantic tropics due to potential subtropical to tropical cyclone formation in the open central Atlantic ocean in the days ahead. This marks the fifty-first tropical Atlantic area of interest tracked on this site this year... see area of interest #51 section below for details.
AREA OF INTEREST #51... As typically seen with out-of-season Atlantic tropical development... monitoring the possibility that a forecast mid-latitude deep-layer cyclone gains tropical characteristics... initiating an area of interest for this situation as the major global models have come into remarkable agreement on this situation. The incipient cold core upper trough moved across the central US and into its current northwestern Atlantic position from December 14th through today... and is forecast to dive southeast into the open central Atlantic and amplify into a cut-off upper vortex in the days ahead due to the force of warm core deep-layer ridging to materialize to the north and west in the warm southerly flow ahead of the current eastern Canada frontal cyclone... followed by warm southerly flow ahead of another frontal low that develops over Atlantic Canada over the next 48 hours. During the 48-hour period the eastern divergence zone of the cut-off upper vortex should produce a burst of shower and thunderstorm activity and dropping surface pressures in the vicinity of 32N-42W... with the upper vortex then become quasi-stationary at this location through 72 hours and reeling in the intensifying surface low... resulting in effectively a deep-layer cyclone. Even though sea-surface temps in the area are currently running at a mild 22 deg C... the upper vortex is forecast to be cold (200 mb heights below 1200 dekameters) resulting in a thermal profile conducive for instability... showers... and thunderstorms. Most of the major global models have come into strong agreement in at least transition into subtropical status... and perhaps fully tropical status should the thunderstorms release enough latent heat to produce a warm core outflow layer above the surface (but below the upper vortex) which would help with surface pressure falls further. Therefore I have already begun with peak 30% odds of subtropical cyclone formation for this new area of interest... and will issue higher odds in future updates should the model consensus remain and/or future satellite observations warrant.
Beyond 72 hours... this system becomes increasingly entangled with a strong upper trough and surface frontal system that encroaches from the western Atlantic. The southerly flow ahead of the surface front should pull the surface low north into increasingly cooler waters less conducive for tropical development... and I lower tropical development odds from the peak in as soon as 96 hours (note the upper vortex over the surface low opens into a NW/SE tilting upper trough while attempting to merge with the encroaching western Atlantic upper trough... should the surface low line up with the western convergence zone of the titling upper trough that would aid in the surface low's weakening). By 120 hours the surface low... if it is still around during that time... should lose its identity to the low pressure field of the incoming western Atlantic surface front.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
IOH 24 Hr Outlook (1800Z Dec 18)... 0% chance of subtropical cyclone formation (central Atlantic near 32N-42W)
IOH 48 Hr Outlook (1800Z Dec 19)... 20% chance of subtropical cyclone formation (central Atlantic near 32N-42W)
IOH 72 Hr Outlook (1800Z Dec 20)... 30% chance of subtropical cyclone formation (central Atlantic near 32N-42W)
IOH 96 Hr Outlook (1800Z Dec 21)... 10% chance of subtropical cyclone formation (central Atlantic near 33.5N-42W)
IOH 120 Hr Outlook (1800Z Dec 22)... 0% chance of subtropical cyclone formation (central Atlantic near 40N-40W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 1 PM EDT*************************
Not in the official outlook
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Dec 17) CMC Model Run...
**For area of interest #51... surface low forms near 29N-40.5W at 60 hours... moves west then southwest through 96 hours while not gaining much strength... surface low weakens to a trough near 27.5N-46W at 126 hours which dissipates shortly thereafter
0000Z (Dec 17) ECMWF Model Run...
**For area of interest #51... surface low forms near 31.2N-40W at 66 hours... rapid subtropical to tropical cyclone formation suggested near 30.5N-43W at 78 hours... the quasi-stationary tropical cyclone then begins to gradually weaken through 120 hours... while turning north weakens to a remnant low near 33N-44W at 138 hours... remnant low loses identity to developing frontal low to the west by 156 hours
1200Z (Dec 17) GFS Model Run...
**For area of interest #51... surface low forms near 32N-39.5W at 48 hours... rapid subtropical to tropical cyclone formation suggested near 32.5N-41W at 57 hours... tropical cyclone moves west-southwest to 31.5N-42.5W through 78 hours... while turning north the tropical cyclone weakens to a remnant low near 34.5N-41.5W by 114 hours... remnant low loses identity ahead of incoming frontal system to the west shortly thereafter
0600Z (Dec 17) NAVGEM Model Run...
**For area of interest #51... surface low forms near 29.5N-38.8W at 54 hours... rapid subtropical cyclone formation suggested near 30N-41W at 66 hours... subtropical cyclone meanders southwest while potentially gaining fully tropical status and reaches 25N-46.5W by 168 hours.
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