*******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.*********
...UPDATE...FRIDAY OCTOBER 27 2023 11:22 AM EDT...
The birdseye view chart below has been updated to include the surface and upper air analysis for 1800Z October 26 which were effective at the time the forecasts and discussions below were created.
Regarding the remnant cyclone of Tammy located just east of Bermuda... the concentrated thunderstorm activity near the center that was occurring early this morning has waned in intensity but is sufficient for the National Hurricane Center to re-instate advisories on Tammy as a fully tropical storm as of 11 AM EDT today. Maximum sustained winds in the latest advisory are 65 mph with a central position of 32.2N-61.1W. Will do a special update within the next couple of hours with more forecast details on the re-generated tropical storm.
...FRIDAY OCTOBER 27 2023 2:10 AM EDT...
Hurricane Tammy has transitioned into a strong non-tropical frontal cyclone east of Bermuda... however it appears there is a high chance that Tammy will soon return to tropical cyclone status as it has re-developed strong thunderstorms near the center. Regardless of its status (tropical or non-tropical)... this system will produce coastal surf and gusty winds over Bermuda over the next 24 hours while drifting westward closer to Bermuda... see area of interest #50 (remnants of Tammy) section below for more information.
Elsewhere noting the following disturbances:
(1) A currently weak tropical wave of low pressure over the southeastern Caribbean could evolve into a more bonafide tropical disturbance as it moves northwestward across Hispaniola (Haiti and the Dominican Republic) and southeastern Bahamas... see area of interest #49 section below for more details.
(2) The remnants of Atlantic basin tropical depression twenty-one (ex-TD 21) in the far eastern Pacific have not become better organized due to easterly shear being imparted by the south side of the current Gulf of Mexico upper ridge cell. However computer models insist ex-TD 21 has a high chance of becoming an eastern Pacific tropical cyclone... and there is now a higher chance that this system will move back northeastward toward Central America and the Caribbean instead of continuing westward around a forecast western North America surface ridge while potentially becoming attracted toward a forecast central Caribbean low pressure tagged as area of interest #51 in this update. If ex-TD 21 does indeed return into the Caribbean... it would most likely merge with area of inerest #51 and not need to be decleared a seperate Caribbean area of interest. Regarding area of interest #51 itself... the area of interest is forecast to lift northward toward Jamaica and eastern Cuba in the days ahead... see area of interest #51 section below for more information.
AREA OF INTEREST #49... The tropical wave of low pressure that was in the vicinity of the southern Lesser Antilles is now in the southeastern Caribbean Sea based on the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Over the next 72 hours the wave is expected to continue generally northwestward in the flow between the surface ridge now departing the eastern US and broad tropical low pressure expected to develop in the central Caribbean... see area of interest #51 section below for more info on the forecast broad tropical low. In the upper-levels an elongated cold core upper vortex to the west is forecast to gradually decay into a pair of dissipating upper vortices due to prolonged isolation from high-latitude cold air. The CMC has recently joined the GFS in suggesting development of this disturbance while this disturbance potentially transitions into a surface trough supported by the southeastern divergence zone of the northern of the pair of fading upper vortices... or over/near the southeastern Bahamas. For 96+ hours... a majority of the upper trough driving the current frontal system heading into the Great Lakes will remain trapped over the United States and develop another frontal system with its divergence zone. As this additional frontal system pushes offshore... the forecast track of this disturbance curves northward and then northeastward away from the Bahamas while chasing the surface ridge weakness of the frontal system. Regarding odds of tropical cyclone formation... I support low peak odds of development for now given the initial weak state of the disturbance. However with model support increasing (with the CMC joining the GFS)... I have raised my peak odds of development to 20% in this update cycle.
This system may develop thunderstorm activity in the days ahead... as such periods of heavy rainfall will be possible in the vicinity of the forecast track within the next few days (Puerto Rico... Haiti... the Dominican Republic... and southeastern Bahamas).
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 28)... 0% chance of tropical cyclone formation (eastern Caribbean Sea near 15N-66W)
IOH 48 Hr Outlook (0000Z Oct 29)... 0% chance of tropical cyclone formation (just south of the Dominican Republic near 17.5N-70W)
IOH 72 Hr Outlook (0000Z Oct 30)... 10% chance of tropical cyclone formation (southeastern Bahamas near 21N-72W)
IOH 96 Hr Outlook (0000Z Oct 31)... 20% chance of tropical cyclone formation (just northeast of the central Bahamas near 25N-74W)
IOH 120 Hr Outlook (0000Z Nov 1)... 20% chance of tropical cyclone formation (western Atlantic near 27.5N-72.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Not in the official outlook
AREA OF INTEREST #50 (REMNANTS OF TAMMY)... Hurricane Tammy has undergone rapid changes over the last couple of days while situated east of Bermuda due to interaction with a western Atlantic upper trough that has fractured into multiple pieces. The northern-third of the upper trough has zoomed eastward and gone on to support the current northeastern Atlantic frontal cyclone... the central-third of the upper trough is lingering just northwest of Tammy... and the southern-third of the upper trough has become an elongated cut-off upper vortex just west of Tammy. From 11 AM EDT Wednesday to 5 AM EDT Thursday the hurricane weakened from its peak of 105 mph maximum sustained winds to 85 mph maximum sustained winds while also transitioning into a non-tropical frontal cyclone. The transition occurred as the hurricane lost its eye and warm core of thunderstorms while ingesting cooler drier air associated with the adjacent upper vortex and also while the hurricane moved into cooler waters below 26 deg C. Shortly after the transition occurred... the remnant cyclone of Tammy has already gone on to re-develop thunderstorms near the center with the aid of split flow upper divergence between easterlies streaming into the north side of the upper vortex and southwesterlies ahead of the upper trough lingering to the northwest. As of 0000Z this evening the remnant cyclone of Tammy was centered near 31.5N-60W while ASCAT-B and ASCAT-C descending passes show wind vectors exceeding 50 knots or 60 mph (https://manati.star.nesdis.noaa.gov/datasets/ASCATCData.php). The ASCAT data suggests the split flow upper divergence is also helping ex-Tammy keep significant gale strength just below hurricane fore. Over the next 24 hours the split flow upper divergence is forecast to persist... and given the concentration of thunderstorms near the center I assess an 80% chance that Tammy re-acquires tropical cyclone status during this period. Ex-Tammy will also be drifting westward closer to Bermuda in the short-term as surface ridging persists to the north under the back convergence zone of upper vorticity now ejecting from the north Canada upper vortex and while ex-Tammy is drawn into the north side of the adjacent upper vortex.
For the middle part of the 5-day forecast period... from 24 to 72 hours... a chunk of the current warm core Gulf of Mexico upper ridge evolves into a warm core northwest Atalntic deep-layer ridge due to the warm air transport out ahead of the developing frontal system now heading for the Great Lakes and eastern Canada. The lingering upper trough currently just northwest of ex-Tammy is forecast to shift east while shoved by the expanding deep-layer ridge while a surface ridge weakness opens from the approaching frontal system. The combination of the eastward-shifting upper trough and the eastward-shifting surface ridge weakness should cause ex-Tammy to reverse eastward away from Bermuda and into the open central Atlantic... with a southward slant in the east track also possible due to the expanding deep-layer ridge. The deep-layer ridge is likely to pin down ex-Tammy such that it falls behind the eastward speed of the upper trough... causing an increase in westerly shear and then exposing ex-Tammy to suppressing convergence on the back western side of the upper trough and southeast side of the deep-layer ridge. Thus my odds of tropical cyclone formation for ex-Tammy during this period are on the low side.
For the end of the 5-day forecast period... from 72 to 120 hours... the northwest Atlantic deep-layer ridge passes north of ex-Tammy... causing ex-Tammy to shift southward... westward... then northwestward around the south side of the passing ridge. The southward dip in the track places the system back over warmer 26 deg C waters... and the upper layers of the deep-layer ridge featuring low shear and upper outflow have potential to overspread ex-Tammy. Therefore my odds of tropical cyclone formation are pulled back up during this period.
For Bermuda... coastal surf will continue for the next 48 hours until ex-Tammy makes its forecast acceleration to the east and away. The updated forecast track does not have ex-Tammy's center passing over Bermuda such that wind damage potential is lower... however ex-Tammy will be near enough by 24 hours (late Friday/early Saturday) to produce an increase in gusty winds and isolated wind damage cannot be ruled out.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 28)... 80% chance of tropical cyclone formation (just east-southeast of Bermuda near 31.5N-62.5W)
IOH 48 Hr Outlook (0000Z Oct 29)... 30% chance of tropical cyclone formation (east-southeast of Bermuda near 31.5N-60W)
IOH 72 Hr Outlook (0000Z Oct 30)... 30% chance of tropical cyclone formation (central Atlantic near 30.5N-55W)
IOH 96 Hr Outlook (0000Z Oct 31)... 40% chance of tropical cyclone formation (central Atlantic near 28N-55W)
IOH 120 Hr Outlook (0000Z Nov 1)... 50% chance of tropical cyclone formation (central Atlantic near 29N-57W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 50%
Formation chance through 7 days... 50%
AREA OF INTEREST #51... An elongated upper vortex is currently present over the Caribbean Sea and western Atlatnic while a warm core Gulf of Mexico upper ridge persists. Split flow upper divergence between these two upper features is producing widespread thunderstorms across Panama and adjacent Caribbean and eastern Pacific waters. The upper vortex is forecast to gradually decay into a pair of dissipating upper vortices due to prolonged isolation from high-latitude cold air. Through 72 hours... models currently insist that any surface low pressure area that develops from the current activity in the vicinity of Panama will lift north and evolve into a broad tropical low pressure in the central Caribbean while aligning with the supportive eastern divergence zone of the southern decaying upper vortex. By 96+ hours the decaying upper vortex begins to shift north in the flow ahead of an upper trough persisting over the United States... and the ongoing northward track of this disturbance is expected while it chases the divergence zone of the upper vortex. The northward track in the long range is also supported while chasing the combined surface ridge weakness of a frontal system to be supported by the United States upper trough and above-discussed area of interest #49. Regarding odds of tropical cyclone formation... I agree with the NHC's low peak of 20% as most model runs currently show the development of a broad low pressure area rather than a bonadfide tropical cyclone. Given the current outlook on this system... the area most likely to receive heavy rainfall within the next few days would be eastern Cuba and Jamaica. The Cayman Islands located further west would most likely be shielded from heavy rain due to shear imparted by the nearby decaying upper vortex.
Update as of 2 AM EDT... the NHC has raised peak odds of tropical cyclone formation of this area of interest to 30%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 28)... 0% chance of tropical cyclone formation (southern Caribbean near 11N-79.5W)
IOH 48 Hr Outlook (0000Z Oct 29)... 0% chance of tropical cyclone formation (southern Caribbean near 12.5N-79.5W)
IOH 72 Hr Outlook (0000Z Oct 30)... 10% chance of tropical cyclone formation (central Caribbean near 15N-79.5W)
IOH 96 Hr Outlook (0000Z Oct 31)... 20% chance of tropical cyclone formation (just southwest of Jamaica near 17.5N-79.5W)
IOH 120 Hr Outlook (0000Z Nov 1)... 20% chance of tropical cyclone formation (between the Cayman Islands and southeast Cuba near 20N-79W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 20%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
1200Z (Oct 26) CMC Model Run...
**For area of interest #49... surface trough becomes better defined just east of the eastern Bahamas at 78 hours... evolves into a surface low that moves into the central Bahamas through 96 hours... surface low then lifts north to 26N-74W through 120 hours.
**For area of interest #50... remnant cyclone of Tammy reaches waters just east of Bermuda by 36 hours while centered near 31.8N-62.5W... subsequently reverses to an east-southeast track while gradually weakening and reaches 30N-53.5W at 84 hours... continues weakening while then curving southwestward and reaches 26N-56.2W at 120 hours.
**For area of interest #51... remnants of tropical depression twenty-one redevelop as an eastern Pacific tropical cyclone near 10.2N-86.2W at 36 hours... subsequently drifts northeastward into western Nicaragua through 90 hours where it weakens to a remnant low... the broadening remnant low continues norhteastward and emerges into the western Caribbean just offshore of eastern Honduras through 120 hours
1200Z (Oct 26) ECMWF Model Run...
**For area of interest #49... no development shown
**For area of interest #50... remnant cyclone of Tammy reaches waters just east of Bermuda by 30 hours while centered near 31.5N-61.5W... subsequently accelerates east and then east-southeast and reaches 30N-46W at 90 hours... then curves southward and reaches 25.5N-45W at 120 hours
**For area of interest #51... broad surface low develops in the central Caribbean Sea near 13N-77W at 54 hours... broad surface low then lifts northward into Jamaica and eastern Cuba through 120 hours.
1800Z (Oct 26) GFS Model Run...
**For area of interest #49... surface trough becomes better defined just east of the eastern Bahamas at 66 hours with tropical cyclone formation suggested just northeast of the eastern Bahamas and near 23.2N-71W at 78 hours... tropical cyclone lifts north to 28.5N-71.2W through 120 hours
**For area of interest #50... remnant cyclone of Tammy reaches waters just east of Bermuda by 30 hours while centered near 32N-62W... subsequently accelerates east and then southeast while gradually weakening and reaches 30N-52.5W at 84 hours... continues weakening while then drifting southwestward and reaches 28.8N-53.8W at 120 hours
**For area of interest #51... no development shown
1800Z (Oct 26) NAVGEM Model Run...
**For area of interest #49... no development shown
**For area of interest #50... remnant cyclone of Tammy reaches waters just southeast of Bermuda by 36 hours while centered near 31N-64W... subsequently drifts slowly southeast while weakening to a surface trough near 30N-60W through 120 hours
**For area of interest #51... surface low develops on the north coast of Honduras at 96 hours... while lifting north into the western Caribbean tropical cyclone formation suggested near 19N-85W at 150 hours
**Surface trough currently near 12N-47W moves west-northwest across the central tropical Atlantic and reaches the northern Lesser Antilles by 168 hours while evolving into a tropical low