*******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...MONDAY OCTOBER 16 2023 11:00 AM EDT...
The birdseye view chart below has been updated to include the surface and upper air analysis for 1800Z October 15 which were effective at the time the forecasts and discussions below were created.
...MONDAY OCTOBER 16 2023 3:10 AM EDT...
Note the usual surface and upper air analysis are not included in the above chart to ensure a more timely release of this update... those parts of the chart will be added later today.
For the tropical latitudes of the Atlantic Ocean to the east of the Lesser Antilles... tropical cyclone Sean has degenerated into a remnant low... with the remnants expected to move into the western Atlantic to the north of the Lesser Antilles over the next five days... see remnants of Sean section below for more information. To the east-southeast of Sean... a vigorous tropical wave of low pressure will remain parked in favorable upper winds while moving toward the Lesser Antilles over the next five days and remains at high risk of tropical cyclone formation... see area of interest #45 section below for more information.
For the northwestern Caribbean Sea... over the next few days the tail end of a surface cold front is expected to pivot from its current position in the Bay of Campeche and into the region while degenerating into a surface trough. Enough tropical upper ridging with low shear and outflow may remain over this region to allow for the development of thunderstorm activity over the surface trough... and it is possible another tropical area of interest may emerge in the northwestern Caribbean Sea within the next few days.
TROPICAL DEPRESSION SEAN (RECENTLY DOWNGRADED TO REMNANTS OF SEAN)... Northward warm air transport ahead of the frontal low now in the western Atlantic is expected to amplify the current central Atlantic upper ridge. The current eastern Atlantic surface ridge is expected to also retrograde westward toward the southeastern convergence zone of the upper ridge to make a deep-layer ridge to Sean's north... which should bend this system's west-northwest track to a more westward heading. This upper convergence zone has also been suppressing Sean and as of 11 PM EDT it was finally downgraded to a remnant low by the NHC. Going forward the remnants of Sean may later take advantage of low shear and outflow beneath the west side of the deep-layer ridge... and hence may require monitoring for re-genesis into a tropical cyclone which is why I have created a 5-day track forecast in this update in preparation for possible tropical cyclone formation probabilities in future updates. Through 48 hours the track keeps Sean's track more westward and less northward as the deep-layer ridge solidifies. The northward angle in the track is then increased after 48 hours once Sean encounters the surface ridge weakness associated with the current central US upper trough... once that trough later moves offshore into the western Atlantic. However there is a westward component to the northward track through 120 hours as most of the western Atlantic upper trough lifts out to the northeast which allows the surface ridge supported by the back side of the upper trough to fill in and prevent a complete northward turn of ex-Sean. The best window for ex-Sean to potentially redevelop into a tropical cyclone is over the next 96 hours as it would encounter increased westerly shear from the next upper trough to approach from North America after that time.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Oct 15)... 30 mph maximum sustained wind tropical depression centered in the central tropical Atlantic at 18N-48.2W
IOH 24 Hr Forecast (1800Z Oct 16)... Remnant trough located in the central tropical Atlantic near 19N-52W
IOH 48 Hr Forecast (1800Z Oct 17)... Remnant trough located northeast of the northern Lesser Antilles near 20N-57.5W
IOH 72 Hr Forecast (1800Z Oct 18)... Remnant trough located north of the northern Lesser Antilles near 21.5N-63W
IOH 96 Hr Forecast (1800Z Oct 19)... Remnant trough located in the western Atlantic near 25N-65W
IOH 120 Hr Forecast (1800Z Oct 20)... Remnant trough located in the western Atlantic near 27.5N-69W
******National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***************************
Loss of Tropical Cyclone Status (0600Z Oct 16)... 30 mph maximum sustained wind remnant low centered in the central tropical Atlantic at 18.2N-49.9W
AREA OF INTEREST #45... The vigorous tropical wave of low pressure following behind Sean has slowed down its westward track and has degenerated into a larger and less organized tropical low pressure area while it merges with another tropical wave of low pressure that has closely following behind to the east. Going forward a central Atlantic deep-layer ridge is expected to materialize as discussed in the above Sean forecast discussion... with this system and pair of upper vorticity lobes to the west and east continuing westward in tandem while pushed around by the deep-layer ridge. This outlook means this system will remain in a favorable upper air envrionment while parked in low shear and upper outflow between the upper vorticity lobes... and most global model runs still develop this system into a tropical cyclone despite the above-noted setback. Therefore I am continuing a tropical cyclone formation forecast with a specific track and intensity projection despite the recent setback... however with a notably lower intensity forecast which gives the next 48 hours for this now-broad system to consoldiate into a tropical cyclone... followed by a more gradual intensification rate as this system could then continue on as a broad tropical cyclone lacking a well-organized inner core. The updated track forecast takes into account the recent slower westward track this system has had... but brings the westward speed back up once it finishes absorbing the adjacent wave to the east and comes under the influence of the central Atlantic deep-layer ridge. The northward angle in the track is increased after 48 hours due to an embedded ridge weakness caused by the tail end of the current western Atlantic to Gulf of Mexico cold front which will be hanging out over the northwestern Caribbean and western Atalntic through day 5 as a remnant surface trough. The western lobe of upper vorticity will also stop moving westward and settle over the eastern Caribbean by day 5 once it reaches the western extent of the steering deep-layer ridge... allowing this system to catch up to the upper vorticity and perhaps be bent more northward by it should it indeed become a stronger/taller system more coupled with upper winds.
Interests in the Lesser Antilles remain aware of this system as it has potential to move toward the islands as a tropical cyclone over the next five days.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Oct 16)... Tropical low centered in the eastern tropical Atlantic at 10N-36.2W
IOH 24 Hr Forecast (0000Z Oct 17)... Tropical low centered in the central tropical Atlantic at 10.5N-40W
IOH 48 Hr Forecast (0000Z Oct 18)... 35 mph maximum sustained wind tropical depression centered in the central tropical Atlantic at 11N-45W
IOH 72 Hr Forecast (0000Z Oct 19)... 50 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 12N-50W
IOH 96 Hr Forecast (0000Z Oct 20)... 65 mph maximum sustained wind tropical storm centered east of the Lesser Antilles at 13N-55W
IOH 120 Hr Forecast (0000Z Oct 21)... 75 mph maximum sustained wind hurricane centered just east-southeast of the northern Lesser Antilles 15.5N-60W
******National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 70%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
0000Z (Oct 15) CMC Model Run...
**For Tropical Depression Sean... weakens to a remnant trough that continues west-northwest into the western Atlantic and reaches 25.5N-69.5W at 120 hours
**For area of interest #45... tropical cyclone formation suggested near 14.5N-46W at 72 hours... moves west-northwest toward the northern Lesser Antilles through 120 hours as a hurricane while reaching 17N-57.5W
0000Z (Oct 15) ECMWF Model Run...
**For Tropical Depression Sean... weakens to a dissipating trough in the next 12 hours
**For area of interest #45... organizes into a tropical low near 11.5N-49W at 90 hours... becomes a tropical depression near 14N-54.5W at 120 hours
1200Z (Oct 15) GFS Model Run...
**For Tropical Depression Sean... weakens to a remnant low through 24 hours while reaching 19N-50.5W... weakens to a remnant trough near 20N-57W at 54 hours... remnant trough reaches 27.5N-69.5W by 120 hours
**For area of interest #45... tropical cyclone formation suggested near 13.8N-52W at 108 hours... tropical cyclone reaches 14.2N-54W through 120 hours
0600Z (Oct 15) NAVGEM Model Run...
**For Tropical Depression Sean... weakens to a remnant low near 21N-55W through 54 hours... remnant low curves northward into the waters just southeast of Bermuda through 120 hours
**For area of interest #45... tropical cyclone formation suggested near 14.5N-48.5W at 78 hours... tropical cyclone strengthens to a high-end tropical storm that reaches 18N-55.5W through 120 hours