*******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...TUEDSAY OCTOBER 31 2023 10:00 AM EDT...
The birdseye view chart below has been updated to include the surface and upper air analysis for 1200Z October 28 which were effective at the time the forecasts and discussions below were created.
...MONDAY OCTOBER 30 2023 2:44 PM 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 within the next several hours.
Tropical Storm Tammy... located in the open central Atlantic... has degenerated into a remnant low within the last 36 hours due to hostile upper-level winds... however this meandering system may find better upper winds over the next few days and hence has a chance to make yet another comeback as a tropical cyclone... see area of interest #52 section below for more information.
Elsewhere noting the following disturbances:
(1) A surface trough of low pressure northeast of the Bahamas is running out of time to become a tropical cyclone... see area of interest #49 for details.
(2) Surface pressures across a large area of the Caribbean Sea remain low... continuing to monitor the Caribbean for tropical cyclone formation in the days ahead... see area of interest #51 section below for more information.
AREA OF INTEREST #49... The surface trough of low pressure that was over the northeastern Caribbean Islands has spent the last 36 hours continuing northwestward into the western Atlantic waters just northeast of the Bahamas while steered in the flow between the northwest Atlantic deep-layer ridge passing to the north and central Caribbean surface low noted in the area of interest #51 section below. As it did so this system had to contend with a string of decaying upper vorticity in the region which has recently collapsed to a pair of fading upper vortices... one also northeast of the Bahamas and another over the southeastern Gulf of Mexico. Noting that a Caribbean upper ridge cell has been expanding the wake of the collapsing upper vortices while also now pushing the upper vortices around. As such the nearby upper vortex northeast of the Bahamas began shifting eastward which increased the westerly shear and displaced the bulk of the surface trough's thunderstorms away from land areas and to the northeast of the Dominican Republic. The disruptive westerly shear has prevented tropical cyclone formation within the surface trough so far... however noting that a cloud swirl surface low has recently developed just east of the northwestern Bahamas (near 25.5N-75W as of 1200Z) in an area of low shear between the pair of upper vortices. So far thunderstorm activity has been minimal with the cloud swirl... and time is running out for tropical cyclone formation as the current United States upper trough will kick the southeastern Gulf of Mexico upper vortex toward this system by 24 hours which will bring hostile westerly shear levels back up. Therefore I have lowered peak odds of tropical cyclone formation to 10% in this update cycle. By 48 hours the United States upper trough will be nearing which will result in a further increase in westerly shear... the forecast position of this system will be over cooler waters below 26 deg C... and moreover the surface cold front driven by the upper trough will have likely absorbed this system. Therefore the 48-hour mark is where I end the oulook with 0% development odds. Forecast track through 24 hours is a north-northwest drift toward the surface ridge weakenss associated with the approaching surface cold front... with a turn to the northeast between 24 and 48 hours in the flow ahead of the front.
Impacts to land areas from this system have ended as the shear is keeping the thunderstorm activity away from land.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 31)... 10% chance of tropical cyclone formation (northeast of the northwestern Bahamas near 28.5N-75.5W)
IOH 48 Hr Outlook (1200Z Nov 1)... 0% chance of tropical cyclone formation (western Atalntic near 31N-71W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 20%
AREA OF INTEREST #51... Surface pressures are low across a wide area of the Caribbean Sea. The first responsible feature is a central Caribbean surface low that formed near Panama within the last few days which has since drifted north-northeastward toward Jamaica while chasing the surface ridge weakness associated with area of interest #49... see birdseye view post #107 for the origins of this surface low (https://www.infohurricanes.com/post/my-2023-atlantic-hurricane-season-birdseye-view-post-107). The second is a surface trough of low pressure which has recently moved into the eastern Caribbean Sea... a study of CIMSS 850 mb vorticity animation (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=) and satellite imagery suggests this new surface trough originated around 0000Z October 29 in a cluster of thunderstorms east of the southern Lesser Antilles enhanced by split flow upper divergence between the southeast corner of the current Caribbean upper ridge cell and southwest corner of a string of persistent central tropical Atlantic upper vorticity. The new surface trough then moved west-northwest into the eastern Caribbean Sea while attracted toward the combined surface ridge weakness assoicated with the aforementioned central Caribbean surface low and area of interest #49. My updated forecast track below assumes the central Caribbean surface low and eastern Caribbean surface trough will spend the next 48 hours merging just south of Hispaniola (Haiti and the Dominican Republic)... followed by a west-southwest track toward Central America beyond that time under the influence of the rather strong surface ridge now approaching from the western US. Even if this system were to become stronger/taller to couple with upper winds... the initial south slant in the forecast track from the push of the strong surface ridge will move this system into the south side of the Caribbean upper ridge where the upper flow is forecast to also be east-northeasterly (ENE)... particularly as some of the central tropical Atlantic upper vorticity tries to retrograde around the south side of the Caribbean upper ridge and toward this system... with the incoming upper vorticity from the east modulating the upper wind vectors from easterly (E) to east-northeasterly (ENE). Regarding peak odds of tropical cyclone formation... I have kept mine at a low 20% and hence lower than the NHC outlook as of this writing as not all global models develop this system... this system may struggle to develop a well-defined center while in an initially broad state caused by the merger between the central Caribbean surface low and eastern Caribbean surface trough... and as this system may have to contend with ENE shear while being on the south side of the Caribbean upper ridge cell rather than underneath it.
Given the updated forecast... the area most likely to see rainfall from this systme within the next few days includes Puerto Rico... the Dominican Republic... Haiti... eastern Cuba... and Jamaica. By day 5 the rainfall potential shifts southwest toward Nicaragua and Honduras... this is also the area most likely to see tropical cyclone impacts (gusty winds and coastal surf) should tropical cyclone formation in fact occur.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 31)... 0% chance of tropical cyclone formation (south of the Dominican Republic near 15.5N-70W)
IOH 48 Hr Outlook (1200Z Nov 1)... 0% chance of tropical cyclone formation (south of the Haiti/Dominican Republic border near 15.5N-72W)
IOH 72 Hr Outlook (1200Z Nov 2)... 10% chance of tropical cyclone formation (south of Haiti near 15.5N-74W)
IOH 96 Hr Outlook (1200Z Nov 3)... 20% chance of tropical cyclone formation (south of Jamaica near 15N-77W)
IOH 120 Hr Outlook (1200Z Nov 4)... 20% chance of tropical cyclone formation (offshore of northeastern Nicaragua near 14.5N-81.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 60%
AREA OF INTEREST #52 (REMNANTS OF TAMMY)... Over the last 36 hours Tammy in the open central Atlantic weakened to a remnant cloud swirl surface low void of thunderstorms due to a one-two punch of wind shear induced by a passing upper trough in the region... followed by suppressing upper convergence on the back western side of the upper trough and southeast side of the northwest Atlantic warm-core deep-layer ridge (the ridge was initialized by warm air transport ahead of the frontal low that recently ejected from eastern Canada... and is now being maintained by the warm sector of the latest frontal low now over the eastern US). As of 1200Z this morning the remnant low was centered at 27.5N-48W. The steering deep-layer ridge so far has bent Tammy's track southeastward... and as the ridge passes to the north the track should reverse to a southwestward and then northwestward direction through 72 hours. The updated forecast track is adjusted southward overall based on Tammy's current position and latest model guidance. On this track... the remnant low will remain below suppressing upper convergence for another 24 hours. However by 48 and 72 hours Tammy is on track to move below the southwest quadrant of the deep-layer ridge's upper layer where wind shear is low and upper outflow is increased... therefore I assign odds of tropical cyclone formation above 0% for that timeframe. However I keep development odds low as the global models as of this writing do not call for ex-Tammy to make a comeback. Between 72 and 96 hours the surface frontal zone currently over the eastern US and its associated upper trough will have moved into the Atlantic... with the flow ahead of these features turning Tammy northeastward. If Tammy does indeed live beyond 72 hours... it has some potential to be absorbed by the incoming cold front by 96 hours. The southward-adjusted forecast track also means that Tammy could also miss the front and meander back on a westward drift due to the surface ridge behind the front... however in that scenario Tammy's potential for re-development would likely be ended due to arrival into shearing mid-latitude upper westerly winds. As such the outlook below is ended at 96 hours with 0% development odds.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
IOH 24 Hr Outlook (1200Z Oct 31)... 0% chance of tropical cyclone formation (central Atlantic near 25N-50W)
IOH 48 Hr Outlook (1200Z Nov 1)... 10% chance of tropical cyclone formation (central Atlantic near 25N-54W)
IOH 72 Hr Outlook (1200Z Nov 2)... 10% chance of tropical cyclone formation (central Atlantic near 28N-57W)
IOH 96 Hr Outlook (1200Z Nov 3)... 0% chance of tropical cyclone formation (central Atlantic near 31N-54.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 2 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 (Oct 30) CMC Model Run...
**For area of interest #49... surface trough evolves into a surface low just east of the northwestern Bahamas through 18 hours... shortly thereafter transitions into an elongated non-tropical frontal low which then intensifies into an elongated frontal cyclone by the time it passes just offshore of Newfoundland at 84 hours... frontal cyclone accelerates east toward Europe and reaches 50.5N-20W by 120 hours.
**For area of interest #51... becomes a better-defined but still broad tropical low in the southern Caribbean near 13N-80W at 120 hours... makes landfall on east coast of Nicaragua at 150 hours
**For area of interest #52... remnant low of Tammy curves southward and then westward and weakens to a trough near 25N-54.5W at 66 hours... trough dissipates shortly thereafter
0000Z (Oct 30) ECMWF Model Run...
**For area of interest #49... surface trough evolves into a surface low just east of the northwestern Bahamas through 18 hours... while drifting northeastward from this location becomes absorbed by developing western Atlantic frontal low to the north by 54 hours.
**For area of interest #51... no development shown
**For area of interest #52... remnant low of Tammy curves southward and then westward and weakens to a trough near 24.5N-51W at 48 hours... trough dissipates shortly thereafter
0600Z (Oct 30) GFS Model Run...
**For area of interest #49... surface trough evolves into a surface low just east of the northwestern Bahamas through 12 hours... while drifting northeastward from this location becomes absorbed by developing western Atlantic frontal low to the north by 48 hours.
**For area of interest #51... current central Caribbean surface low and eastern Caribbean surface trough merge with the eastern side of the merged envelope developing into a tropical cyclone near 13.8N-70W at 69 hours... strengthens into a compact hurricane while moving west-southwest to 13N-79W through 120 hours
**For area of interest #52... remnant low of Tammy curves southward and then westward and weakens to a trough near 24.5N-51W at 45 hours... trough dissipates shortly thereafter
0600Z (Oct 30) NAVGEM Model Run...
**For area of interest #49... becomes absorbed by developing western Atlantic frontal low to the north by 48 hours
**For area of interest #51... no development shown
**For area of interest #52... remnant low of Tammy curves southward and then westward and weakens to a trough near 24.5N-51W at 48 hours... trough dissipates shortly thereafter