*******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.*********
...UPDATE...SATURDAY DECEMBER 21 2024 11:11 PM EDT...
The central Atlantic low pressure swirl is accelerating northward into cooler waters in the flow ahead of an approaching western Atlantic frontal system. As such whatever shower activity it had in its circulation has dissipated and it’s transition into a tropical feature is no longer possible. This is also my final regular update on the Atlantic tropics until the start of the 2025 Atlantic Hurricane Season in June… or unless another system with tropical development potential emerges in the Atlantic basin before then.
...UPDATE...FRIDAY DECEMBER 20 2024 9:38 AM EDT...
After whirling further west overnight as forecast... the surface low pressure swirl in the open central Atlantic has already slipped back east toward 32N-42W as of this morning while becoming pulled into the core of the upper vortex. It does not appear the upper vortex is cold enough for instability as the bands of showers in the southern semicircle of the surface low have revolved into the northern quadrant while remaining weak. I have therefore lowered odds of subtropical cyclone formation for 0000Z tonight to 20%... and for 0000Z Dec 22 (tomorrow night) to 0%.
...THURSDAY DECEMBER 19 2024 11:30 PM EDT...
Continuing daily posts on the Atlantic tropics due to potential subtropical to tropical cyclone formation in the open central Atlantic ocean within the next couple of days. See area of interest #51 section below for details.
AREA OF INTEREST #51... More recent satellite image of the central Atlantic surface low being monitored for acquisition of tropical characteristics... image taken as of 0310Z:
A cold core upper trough in the open central Atlantic ocean has recently amplified into a cut-off upper vortex due to adjacent amplification of warm core upper ridging to the north and west. The eastern divergence zone of the vortex has contributed to the quick formation of a surface low pressure near 31N-40W earlier today... which has recently whirled west to 32N-41W as of 0000Z while pulled in by the northeast quadrant of the upper vortex... and as of this writing the surface low has whirled further west to 32N-42W. The upper vortex is expected to settle near 32N-42W over the next 24 hours... therefore the surface low is expected to continue even further west within the northwest quadrant of the upper vortex through tonight... then back east towards 32N-42W by tomorrow evening while pulled into the core of the upper vortex. Even though the surface low is over 22 deg C waters... the upper vortex is cold (200 mb heights below 1200 dekameters) which could result in a thermal profile conducive for instability... showers... and thunderstorms. The surface low has recently pulled in some of the shower and thunderstorm activity that was east of the center into its western then southern quadrant... albeit as of the most recent infrared 0310Z satellite frame shows the activity in the southern quadrant has weakened which could be why this system has still not been introduced into the NHC tropical weather outlook. Therefore in this update cycle I am keeping peak odds of subtropical cyclone formation at 40%.
Beyond 24 hours... this system becomes increasingly entangled with a strong upper trough and surface frontal system currently over the central US which will quickly slide into and across 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 48 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 72 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 (0000Z Dec 21)… 40% chance of subtropical cyclone formation (central Atlantic near 32N-42W)
IOH 48 Hr Outlook (0000Z Dec 22)… 15% chance of subtropical cyclone formation (central Atlantic near 33.5N-42W)
IOH 72 Hr Outlook (0000Z Dec 23)… 0% chance of subtropical cyclone formation (central Atlantic near 40N-41W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 7 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/).
1200Z (Dec 19) CMC Model Run...
**For area of interest #51... subtropical cyclone formation suggested near 32N-41.5W at 12 hours… lifts north and weakens to a remnant low near 36N-44W at 72 hours… remnant low loses identity to developing frontal low to the west shortly thereafter
1200Z (Dec 19) ECMWF Model Run...
**For area of interest #51... subtropical cyclone formation suggested near 32N-41W at 12 hours… lifts north and weakens to a remnant low near 36.5N-44.5W at 72 hours… remnant low loses identity to developing frontal low to the west shortly thereafter
1800Z (Dec 19) GFS Model Run...
**For area of interest #51... subtropical cyclone formation suggested near 32N-44W at 9 hours and becomes potentially fully tropical by 24 hours while quasi-stationary… lifts north and weakens to a remnant low near 36N-44W at 66 hours… remnant low loses identity to developing frontal low to the west shortly thereafter
1800Z (Dec 19) NAVGEM Model Run...
**For area of interest #51... subtropical cyclone formation suggested near 31N-43W at 12 hours… lifts north and weakens to a remnant low near 34N-44W at 60 hours… remnant low loses identity to developing frontal low to the west shortly thereafter
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