*******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 30 2023 11:31 AM EDT...
The birdseye view chart below has been updated to include the surface and upper air analysis for 1800Z October 28 which were effective at the time the forecasts and discussions below were created.
Regarding Tropical Storm Tammy in the open central Atlantic... the hostile environment of westerly shear followed by upper convergence as noted in the Tammy forecast discussion below has indeed weakened Tammy to a remnant low pressure swirl void of thunderstorms. The final advisory on Tammy from the National Hurricane Center was issued on 5 AM EDT Sunday October 29.
Regarding the surface trough of low pressure that was over the northeastern Caribbean Islands... which was tagged area of interest #49 in the update below... this feature has since moved northwestward into the western Atlantic waters just northeast of the Bahamas. Excess westerly shear... which has been exacerbated as the nearby decaying upper vortex shifted eastward... has since displaced the thunderstorm activity northeastward from all land areas and is preventing tropical cyclone formation of this feature.
...SUNDAY OCTOBER 29 2023 1:14 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 within the next several hours.
Tropical Storm Tammy has turned eastward into the open central Atlantic waters where it will meander over the next few days... see Tammy section below for an update on this system.
Elsewhere noting the following disturbances:
(1) A tropical disturbance currently over the northeastern Caribbean Islands has increased potential to become a tropical cyclone to the northeast of the Bahamas... see area of interest #49 for details.
(2) Refer to the area of interest #51 section below for an update on the central Caribbean tropical low pressure area still forecast to meander toward the north-central Caribbean islands within the next few days.
(3) The remnants of Atlantic basin tropical depression twenty-one (ex-TD 21) in the far eastern Pacific have developed into tropical depression nineteen-E. The latest model guidance suggests nineteen-E will at first drift eastward back toward Guatemala and El Salvador over the next 48 hours while attracted toward the surface ridge weakness associated with Altantic areas of interest #49 and #51... followed by acceleration back westward across the eastern Pacific as the surface ridge currently developing over the western US nears and takes over the steering. Therefore re-entry of this system back into the Caribbean is not anticipated. This system could also become a strong eastern Pacific tropical cyclone while remaining in a favorable environment of low shear... upper outflow... and warm sea surface temperatures. Refer to the NHC website at hurricanes.gov for up to the minute latest information on nineteen-E as this site is focused on Atlantic tropical activity.
TROPICAL STORM TAMMY... Over the last 36 hours Tammy has accelerated eastward away from Bermuda and into the open central Atlantic while moving in tandem with the lingering upper trough to its northwest and surface ridge weakness associated with the frontal low approaching from eastern Canada. The upper trough has tended to shear Tammy's thunderstorms to the east of its swirl center and as a result the tropical storm has been weakening. However the divergence zone of this upper trough may be why Tammy has had just enough thunderstorm activity to still be tropical despite being over waters below 26 deg C. My updated forecast track below is adjusted eastward as the tropical storm has been moving faster to the east compared to the old forecast. The forecast track going forward is an anticyclonic curve in the open central Atlantic that turns increasingly southeastward... then southwestward and northward as a warm core deep-layer ridge materializes in the northwest Atlatnic in the next 24 hours in the warm sector of the frontal low currently over eastern Canada... with the deep-layer ridge then passing north of Tammy with Tammy in turn moving around the passing deep-layer ridge. Because Tammy will be pinned down by the deep-layer ridge soon... it will fall behind the eastward speed of the nearby upper trough and hence become increasingly sheared by the trough... then become exposed to suppressing upper convergence on the back western side of the trough and southeast side of the deep-layer ridge. As a result I forecast Tammy to weaken to a remnant low in the next 24 hours despite re-entry back into 26+ deg C water temps. As the upper layers of the deep-layer ridge later overspreads Tammy with lower shear and upper outflow... Tammy may be in a position to take advantage of the 26+ deg C waters and hence I continue to forecast this system to make yet another comeback as a tropical cyclone in what is now the 48 to 96 hour range. My updated intensity forecast for this window is a little higher than my previous as the updated forecast track keeps Tammy below the favorable upper layer of the deep-layer ridge for longer. However noting my updated intensity forecast is still conservative as the models are not calling for Tammy to re-develop. Between 96 and 120 hours the surface frontal zone currently over the central US and its associated upper trough will have moved into the Atlantic... with the flow ahead of these features accelerating Tammy northeastward. If Tammy does indeed live beyond 96 hours... it should come to a swift end by 120 hours as the incoming surface cold front absorbs Tammy.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Oct 29)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 32.6N-55.2W
IOH 24 Hr Forecast (0000Z Oct 30)... 35 mph maximum sustained wind non-tropical remnant low centered in the central Atlantic at 30.5N-50W
IOH 48 Hr Forecast (0000Z Oct 31)... 35 mph maximum sustained wind tropical depression centered in the central Atlantic at 27.5N-49W
IOH 72 Hr Forecast (0000Z Nov 1)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 27.5N-52W
IOH 96 Hr Forecast (0000Z Nov 2)... 50 mph maximum sustained wind tropical storm centered in the central Atlanic at 30.5N-55W
IOH 120 Hr Forecast (0000Z Nov 3)... Absorbed by cold front while located in the central Atlantic at 36N-50W
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Loss of Tropical Cyclone Status (1200Z Oct 29)... 35 mph maximum sustained wind non-tropical remnant low centered in the central Atlantic at 32N-52W
AREA OF INTEREST #49... The tropical wave of low pressure that was in the eastern Caribbean has moved northwestward across the northeastern Caribbean islands while evolving into a better-established surface trough with increased thunderstorm activity. The northwest track has been induced by the flow between the surface ridge now departing the eastern US and broad tropical low pressure in the central Caribbean... see area of interest #51 section below for more info on the broad tropical low. In the upper-levels an elongated string of cold core upper vorticity to the west has been decaying due to prolonged isolation from high-latitude cold air. The initial eastern divergence zone of the upper vorticity... followed by the expansion of a regional warm core upper anticyclone with upper outflow in the wake of the decaying upper vorticity... likely explains the intensification of this disturabnce to a more bonafide surface trough. However the surface trough is currently not well-organized while featuring multiple rotations... with the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=) showing one area of rotation just northeast of the Dominican Republic and the curvature of thunderstorm bands on colorized infrared satellite pictures suggesting another center of rotation just south of Puerto Rico. The models agree that the center near the Dominican Republic will go on to become the dominant as the decaying upper vorticity string collapses into two upper vortices... with the center near the Dominican Republic getting a boost from the southeastern divergence zone of the northern upper vortex. I have raised my odds of tropical cyclone formation to 30% in this update cycle as this system has indeed gone on to become a better-defined surface trough. However my odds are below the latest NHC outlook guidance due to the initial disorganized state of this system and as this system is likely to be sheared by the decaying upper vortex. Shear will also be imparted by the current upper trough over the United States when that trough later nears... with the flow ahead of the upper trough and associated surface front re-curving this system northeastward away from the Caribbean Islands and Bahamas after 48 hours. My outlook below is ended at the 96 hour mark... with 0% odds of tropical development... as this system moves into water temps below 26 deg C and is absorbed by the surface front.
The thunderstorm activity of this system has brought heavy rains to the Lesser Antilles... Virgin Islands... and Puerto Rico. Based on the latest satellite imagery... additional heavy rains are possible in the short-term for Puerto Rico and the Virgin Islands... spreading across the the Dominican Republic... Haiti... and southeastern Bahamas through 48 hours. Rainfall further west of these locations is unlikely due to the forecast westerly shear noted in the prior paragraph.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 30)... 30% chance of tropical cyclone formation (just north of the southeastern Bahamas near 22.5N-72W)
IOH 48 Hr Outlook (0000Z Oct 31)... 30% chance of tropical cyclone formation (north of the central Bahamas near 26N-74W)
IOH 72 Hr Outlook (0000Z Nov 1)... 30% chance of tropical cyclone formation (western Atlantic near 29N-70W)
IOH 96 Hr Outlook (0000Z Nov 2)... 0% chance of tropical cyclone formation (just northeast of Bermuda near 35N-62.5W)
*****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... The tropical low pressure that formed in the southern Caribbean just north of Panama has been drifting northeastward toward the surface ridge weakness associated with area of interest (AOI) #49. Even though the NHC has removed this feature from their tropical weather outlook... due to its loss of organized thunderstorm activity... I am maintaining this feature as an area of interest as a regional upper anticyclone with favorable low shear and upper outflow is materializing in the wake of the decaying upper vorticity string to the west. In addition the GFS and NAVGEM models suggest this system will last over the next five days while continuing to drift northeastward toward AOI #49... followed by a westward turn as a strong surface ridge now developing from the western US later approaches. The GFS goes as far as suggesting tropical cyclone formation in the long range. My updated forecast track below shows a similar forecast track philosophy to the GFS/NAVGEM consensus. My peak odds of tropical cyclone formation are kept at a low 20% in this update cycle as most model runs do not show explicit tropical cyclone formation... and as this system's initial state is weak and disorganized.
Given the updated forecast track... the area most likely to see rainfall from this system in the next few days continues to include eastern Cuba and Jamaica... with rains from this system now possible as far east as Haiti and the Dominican Republic as well.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 30)... 0% chance of tropical cyclone formation (offshore of northern Colombia near 12.5N-74W)
IOH 48 Hr Outlook (0000Z Oct 31)... 10% chance of tropical cyclone formation (offshore of the Guajira peninsula of Colombia near 14N-72.5W)
IOH 72 Hr Outlook (0000Z Nov 1)... 20% chance of tropical cyclone formation (south of Haiti near 16N-72.5W)
IOH 96 Hr Outlook (0000Z Nov 2)... 20% chance of tropical cyclone formation (just offshore of southwestern Haiti near 17.5N-74W)
IOH 120 Hr Outlook (0000Z Nov 3)... 20% chance of tropical cyclone formation (vicinity of Jamaica near 17.5N-77W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 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/).
1200Z (Oct 28) CMC Model Run...
**For Tropical Storm Tammy... accelerates east-southeast to 28N-45.5W through 54 hours while weakening to a remnant low... remnant low subsequently drifts west-southwest and reaches 27.5N-53.5W at 102 hours where it dissipates.
**For area of interest #49... surface trough currently over the northeastern Caribbean islands becomes a tropical cyclone near 23.5N-70W at 30 hours... subsequently transitions into an elongated remnant low ahead of frontal system emerging from the eastern US while located near 28N-74W at 66 hours... remnant low subsequently accelerates northeastward into Bermuda through 108 hours where it then becomes absorbed by the approaching frontal system
**For area of interest #51... no development shown
1200Z (Oct 28) ECMWF Model Run...
**For Tropical Storm Tammy... accelerates east-southeast to 30N-45.5W through 42 hours while weakening to a remnant low... remnant low then turns southwest while weakening to a surface trough with the trough dissipating near 25N-50W at 102 hours
**For area of interest #49... surface trough currently over the northeastern Caribbean islands becomes an elongated surface low ahead of frontal system emerging from the eastern US while located near 28N-74W at 78 hours... surface low then loses identity within the frontal system shortly thereafter
**For area of interest #51... no development shown
1800Z (Oct 28) GFS Model Run...
**For Tropical Storm Tammy... accelerates east-southeast and then southward to 27.5N-47.5W through 60 hours while weakening to a remnant low... remnant low then turns west and then northward and dissipates near 32N-54W at 108 hours
**For area of interest #49... surface trough currently over the northeastern Caribbean islands becomes an elongated surface low ahead of frontal system emerging from the eastern US while located near 28N-76W at 69 hours... elongated surface low then accelerates north-northeastward while transitioning into a non-tropical elongated frontal cyclone which passes just offshore of Newfoundland at 105 hours and reaches the open north Atlantic near 51.5N-40.5W at 120 hours
**For area of interest #51... central Caribbean surface low currently offshore of Colombia drifts northeastward to waters south of the Dominican Republic through 108 hours while chasing surface ridge weakness associated with AOI #49... subsequently the surface low drifts westward under influence of strong surface ridge that approaches from the western US and develops into a tropical cyclone near 13.5N-70.5W at 150 hours
1800Z (Oct 28) NAVGEM Model Run...
**For Tropical Storm Tammy... accelerates east-southeast and reaches 30.5N-49W through 30 hours while weakening to a remnant low... remnant low then turns southward and then westward and reaches 25.5N-52.5W at 90 hours where it then dissipates
**For area of interest #49... surface trough currently over the northeastern Caribbean islands becomes an elongated surface low ahead of frontal system emerging from the eastern US while located just northeast of the northwestern Bahamas at 72 hours... surface low then loses identity within the frontal system shortly thereafter
**For area of interest #51... central Caribbean surface low currently offshore of Colombia drifts northeastward while chasing surface ridge weakness associated with AOI #49 through 108 hours... subsequently the surface low drifts westward under influence of strong surface ridge that approaches from the western US with the surface low strengthening near 13.5N-77.5W at 150 hours