*******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.*********
...WEDNESDAY NOVEMBER 22 2023 2:35 PM EDT...
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 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 Colombian coast... see area of interest #56 section below for details.
AREA OF INTEREST #54... The current central Atlantic frontal low continues to be monitored for potential tropical development in the days ahead while forecast to dip southeastward toward 26+ deg C waters under the influence of the materializing western Atlantic deep-layer ridge. A southern fragment of the frontal low's supporting upper trough is also forecast to move southeastward. This 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 potential tropical characteristics of the frontal low. After 24 hours... the upstream frontal system currently over the eastern United States 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 72 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 96 hours while merging with another upstream upper trough that approaches from Canada.
Regarding the forecast track... the current position of the frontal low is a little north and east of the previous forecast while located near 30N-47.5W as of 1200Z today... therefore the updated forecast below is adjusted accordingly. Regarding odds of subtropical cyclone formation... it is 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 24 hours... and as the cut-off upper trough then merges with the upstream upper troughs late in the forecast period. The frontal low is also currently elongated and models have recently trended toward an elongated system instead of a cyclone. The NHC has recently lowered peak odds of subtropical cyclone formation to 50% and I have lowered my peak odds to 30%. My peak odds of subtropical cyclone formation are set for 48 hours when this system is least likely to be elongated... i.e. when this system's cut-off upper trough is most isolated from high-latitude upper troughs (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 72 hours the northeastward adjusted forecast track already brings 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%... with 0% development odds by 96 hours once this system vaults into even cooler waters in the vicnity of the Azores
Regardless of subtropical cyclone formation or not... this system has potential to spread heavy rains... gusty winds... and coastal surf across the Azores by Sunday.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Nov 23)... 0% chance of subtropical cyclone formation (central Atlantic near 27.5N-42W)
IOH 48 Hr Outlook (1200Z Nov 24)... 30% chance of subtropical cyclone formation (eastern Atlantic near 28N-38W)
IOH 72 Hr Outlook (1200Z Nov 25)... 10% chance of subtropical cyclone formation (eastern Atlantic near 32.5N-33W)
IOH 120 Hr Outlook (1200Z Nov 26)...0% chance of subtropical cyclone formation (vicinity of Azores near 39N-29.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 1 PM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 50%
AREA OF INTEREST #56... The central Caribbean tropical low offshore of Colombia has moved westward under the influence of the western Atlantic deep-layer ridge and was positioned near 12.5N-77W as of 1200Z. This initial position is southwest of the previous forecast and the updated one below is adjusted accordingly. The ridge weakness of the passing eastern United States frontal system will be too narrow to recurve this system north... instead a west-northwest track of this system is anticipated going forward. The ongoing west angle in track will be caused by the surface ridge that builds behind the passing frontal system while the north slant in the track is caused by a secondary frontal low that develops across the southern Gulf of Mexico (the secondary frontal low develops with the support of an upper trough fragment left behind by the current eastern US frontal system).
Regarding odds of tropical cyclone formation... the distance between the tropical low and dry air associated with the convergence zone of the current central Atlantic upper trough as the two features move in opposite directions... as a result the tropical low has seen a recovery in shower and thunderstorm activity while taking advantage of the outflow of the regional upper ridge and I have increased odds of tropical cyclone formation to 20%. The updated forecast track moves this system into a landfall with Central America (Nicaragua and Honduras) by 72 hours and this is when my updated outlook below is ended. With the updated forecast... periods of heavy rainfall are possible across Nicaragua and Honduras by Friday and Saturday.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Nov 23)... 20% chance of tropical cyclone formation (south-central Caribbean Sea near 13N-80W)
IOH 48 Hr Outlook (1200Z Nov 24)... 20% chance of tropical cyclone formation (just offshore of northeastern Nicarauga near 13.5N-82.8W)
IOH 72 Hr Outlook (1200Z Nov 25)... 0% chance of tropical cyclone formation (inland portion of Nicaragua/Honduras border near 14N-85.5W)
*****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 (Nov 22) CMC Model Run...
**For area of interest #54... frontal low currently near 30N-47.5W continues east while remaining elongated and reaches 29N-36W at 66 hours... frontal low then turns northeast while intensifying into a frontal cyclone that passes just northwest of the Azores through 120 hours
**For area of interest #56... no development shown
0000Z (Nov 22) ECMWF Model Run...
**For area of interest #54... frontal low currently near 30N-47.5W continues east while remaining elongated and reaches 28.5N-40W at 60 hours... frontal low then accelerates north-northeast and elongates further into multiple frontal lows just west of the Azores through 96 hours
**For area of interest #56... no development shown
1200Z (Nov 22) GFS Model Run...
**For area of interest #54... frontal low currently near 30N-47.5W continues southeast with possible subtropical cyclone foramtion near 24.5N-41W at 36 hours... while accelerating northeastward into the Azores through 93 hours the possible subtropical cyclone transitions into a remnant frontal cyclone... frontal cyclone continues northeast to 44N-20W through 120 hours
**For area of interest #56... tropical low continues west-southwest into the waters offshore of the Nicaragua/Costa Rica border through 48 hours... dissipates shortly thereafter
0600Z (Nov 22) NAVGEM Model Run...
**For area of interest #54... frontal low currently near 30N-47.5W loses dominance to developing frontal cyclone to the north through 42 hours
**For area of interest #56... no development shown