*******Note that forecast 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 NOVEMBER 21 2023 1:36 PM EDT...
The upper vortex currently located just south of the Azores has seen a notable increase in thunderstorms over the last 24 hours due to the de-stablizing cold temperatures of this feature. However the surface layer of the regional deep-layer ridge is located to the north and has pushed the nearby surface frontal low westward while the upper layer of the ridge located further to the southwest slows the westward progress of the upper vortex... thus the surface frontal low is no longer aligned with the upper vortex to take advantage of the thunderstorms and gain tropical characteristics.
Elsewhere... continuing to monitor two features in the Atlantic basin for possible tropical development in the days ahead:
(1) A frontal low in the open central Atlantic is forecast to dive east-southeast into waters sufficiently warm for acquisition of tropical characteristics... see area of interest #54 section below for details.
(2) A tropical low pressure spin is currently located in the central Caribbean and just northwest of the Guajira peninsula of Colombia... see area of interest #56 section below for details.
AREA OF INTEREST #54... Continuing to monitor a frontal low now in the open central Atlantic for potential tropical development in the days ahead due to the following forecast:
Over the next 48 hours... the warm sector of the current United States frontal system will amplify the current Caribbean upper ridge cell across the western Atlantic... the eastern convergence zone of which will cause the eastward shift of the current eastern North America surface ridge into the western Atlantic. The end result is a warm core western Atlantic deep-layer ridge that pushes the frontal low of interest and a southern frgament of its upper trough east-southeastward into the open central Atlantic. The cut-off upper trough fragment is expected to be amplified while squashed between the western Atlantic deep-layer ridge and current northeast Atlantic deep-layer ridge. The amplified nature of the cut-off upper trough is expected to result in higher divergence and lower shear on its east side conducive for thunderstorm generation and tropical characteristics of the frontal low of interest... particularly as this system will be moving across the part of the open central Atlantic where water temps are still 26+ deg C. After 48 hours... the upstream frontal system from the United States and its upper trough breaks through the western Atlantic deep-layer ridge... with the cut-off upper trough of this area of interest merging with the upstream upper trough to make a northwest-southeast tilted upper trough that lifts this system northeastward in the long range. The upper trough loses its tilt by 96 hours as the northern part of the upper trough moves faster than the southern part... however the northwest-southeast tilt supporting an ongoing northeastward track of this system returns by 120 hours while merging with another upstream upper trough that approaches from Canada.
Regarding the forecast track... the updated one below is adjusted eastward based on the latest model consensus. Regarding odds of subtropical cyclone formation... I have slightly increased peak odds to 40% as the global model consensus continues to trend toward possible cyclone formation. I have not selected higher odds in this update as it is also possible for this system and its supportive upper divergence region to become too elongated for cyclone status should the southern cut-off upper trough remain too entangled with the northern upper trough fragment through the next 48 hours... and as the cut-off upper trough then merges with the upstream upper troughs late in the forecast period. As such my peak odds of subtropical cyclone formation are set for 72 hours when this system's cut-off upper trough is most isolated from high-latitude upper troughs... i.e. after its seperation from the northern upper trough in the short-term and before its merger with upstream upper troughs in the long term. By 120 hours the forecast track takes this system into waters below 26 deg C... and with upper air temps not very cold (200 mb heights above 1200 dekameters) the thermodynamic profile becomes increasingly stable. For this timeframe I pull down odds of subtropical development to a low 10%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Nov 22)... 0% chance of subtropical cyclone formation (central Atlantic near 29N-50W)
IOH 48 Hr Outlook (1200Z Nov 23)... 30% chance of subtropical cyclone formation (central Atlantic near 26.5N-42.5W)
IOH 72 Hr Outlook (1200Z Nov 24)... 40% chance of subtropical cyclone formation (eastern Atlantic near 26.5N-39W)
IOH 96 Hr Outlook (1200Z Nov 25)... 30% chance of subtropical cyclone formation (eastern Atlantic near 29N-36W)
IOH 120 Hr Outlook (1200Z Nov 26)...10% chance of subtropical cyclone formation (southwest of the Azores near 33.8N-32.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 1 PM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 60%
AREA OF INTEREST #56... The central Caribbean tropical low has become better-defined further southeast and just offshore of the Guajira peninsula of Colombia... or near 13.5N-73W... as a cloud-swirl feature and the updated forecast track below is adjusted accordingly. Over the next 24 hours the tropical low is expected to be pushed west by the ridge. Between 24 and 48 hours a frontal system ejecting from the United States should be passing to the north... however its ridge weakness should be too narrow to recurve this system north. Instead a west-northwest track should ensue for the 48 to 96 hour period... with the ongoing west angle in track caused by the surface ridge that builds behind the passing frontal system and while the north slant in the track is caused by a secondary frontal low that develops across the southern Gulf of Mexico and heads across the Florida peninsula (the secondary frontal low develops with the support of an upper trough fragment left behind by the frontal system ejecting from the United States). Once the secondary frontal low continues east-northeast and away the forecast track is bent more west and less north for the 96 to 120 hour period.
Regarding odds of tropical cyclone formation... global models do not develop this system and the tropical low has lost much of its prior thunderstorm activity due to dry air lurking to the north generated by the western convergence zone of the upper trough tied to area of interest #54... thus I have lowered odds of tropical cyclone formation to 10% now in agreement with the NHC. Through 48 hours the upper trough generating the regional dry air will be shifting eastward and away while this system remains under a vast upper ridge cell with low shear and upper outflow... therefore it is possible for this system to re-develop thunderstorms and thus it is sensible to maintain this system as a tropical area of interest instead of cancelling it with 0% development odds. By 72 and 96 hours the upper trough fragment tied to the aforementioned southern Gulf secondary frontal low increases westerly shear across this system. The shear however is not likely to be excessive as the upper trough fragment passes far north enough which is why I keep development odds above 0% through 96 hours. By 120 hours the shear relaxes as the upper trough fragment then moves away.
Should this system indeed persist through day 5... the most likely impact to land areas would be rainfall across the Cayman Islands from moisture sheared-off from this system by day 4... followed by rainfall across northern Honduras by day 5 as wind shear in the region relaxes.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Nov 22)... 10% chance of tropical cyclone formation (south-central Caribbean Sea near 13.5N-75.5W)
IOH 48 Hr Outlook (1200Z Nov 23)... 10% chance of tropical cyclone formation (south-central Caribbean Sea near 14.5N-79W)
IOH 72 Hr Outlook (1200Z Nov 24)... 10% chance of tropical cyclone formation (east of eastern Honduras near 15.5N-81.5W)
IOH 96 Hr Outlook (1200Z Nov 25)... 10% chance of tropical cyclone formation (just offshore of eastern Honduras near 16N-84W)
IOH 120 Hr Outlook (1200Z Nov 26)... 10% chance of tropical cyclone formation (just offshore of western Honduras near 16N-87.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 1 PM EDT***************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 10%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
0000Z (Nov 21) CMC Model Run...
**For area of interest #54... frontal low currently near 30N-57.5W continues east-southeast with possible subtropical cyclone formation sugested near 25.5N-42W at 60 hours... possible subtropical cyclone then accelerates northeastward to 32.5N-32W thorugh 120 hours
**For area of interest #56... current central Caribbean tropical low moves west-southwest 11.5N-80W through 72 hours while weakening to a trough... trough dissipates shortly thereafter
0000Z (Nov 21) ECMWF Model Run...
**For area of interest #54... frontal low currently near 30N-57.5W continues east-southeast with possible subtropical cyclone formation sugested near 25.5N-46W at 60 hours... possible subtropical cyclone then moves east-northeast and reaches 30N-36.2W at 120 hours
**For area of interest #56... no development shown
0600Z (Nov 21) GFS Model Run...
**For area of interest #54... frontal low currently near 30N-57.5W continues east-southeast with possible subtropical cyclone formation sugested near 24.8N-46.5W at 42 hours... possible subtropical cyclone then continues east then east-northeast and reaches 32N-32.5W at 120 hours
**For area of interest #56... quickly weakens to a surface trough that reaches 12.5N-80.5W at 51 hours... after re-evolving into a tropical low for a short time dissipates just offshore of Nicaragua at 60 hours
0600Z (Nov 21) NAVGEM Model Run...
**For area of interest #54... frontal low currently near 30N-57.5W continues east-southeast with possible subtropical cyclone formation sugested near 25.5N-40.5W at 66 hours... possible subtropical cyclone then moves east-northeast to 32N-33W through 120 hours
**For area of interest #56... no development shown