*******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...TUESDAY OCTOBER 1 2024 2:45 PM EDT...
The surface and upper air panels valid for September 30... which were not previously included in the birdseye view chart below to ensure a timely release of the September 30 update... have now been added. In addition the following events have occurred since yesterday's September 30 update:
(1) Tropical Depression Joyce in the open central Atlantic has weakened to a remnant low due to ongoing wind shear.
(2) Tropical Storm Kirk in the eastern tropical Atlantic has continued to gradually strengthen... and as of this writing is evaluated by the NHC to have 70 mph maximum sustained winds.
...MONDAY SEPTEMBER 30 2024 4:15 PM EDT...
See remnants of Isaac... tropical depression Joyce... and tropical storm Kirk sections below for more information on currently or formerly active tropical cyclones currently positioned in the open parts of the Atlantic basin. In addition monitoring the following areas of interest:
(1) See area of interest #34 for a tropical wave of low pressure which could develop within the next few days in the western Caribbean... southern Gulf of Mexico... and surrounding land areas.
(2) See area of interest #36 section below for the latest eastern Atlantic tropical wave of low pressure now being monitored for possible development in the days ahead (the tag of area of interest #35 was assigned to the wave that became Kirk).
(3) Upper vorticity currently over the eastern United States over the next few days is forecast to move east-southeast toward the western Atlantic waters in Bermuda's proximity... the south angle in the track being aided by warm core upper ridging forecast to be over the United States. The eastern divergence zone of the upper vorticity is expected to trigger an associated surface frontal low... will watch to see if the surface feature acquires tropical characteristics over or near Bermuda in the days ahead (and will upgrade to an area of interest in future updates if necessary).
TROPICAL DEPRESSION JOYCE... After turning north into the ridge weakness associated with the current northwest Atlantic deep-layer frontal cyclone... Joyce has become nearly stationary while in conflicting steering between the current eastern Atlantic surface ridge and western Atlantic deep-layer ridge... and is not an impressive tropical cyclone while weakening to a tropical depression due to wind shear pulling the thunderstorms northeast of the surface cloud swirl. The latest visible satellite loops show the surface swirl of Joyce is drifting slowly northeast and so my updated forecast point for 24-hours is a reflection of this. During this time the southern base of the upper trough associated with the mid-latitude deep-layer frontal cyclone swings east in Joyce's vicinity... switching the wind shear to a more westerly direction and stronger. Therefore I forecast Joyce to weaken to a remnant low in the next 24 hours. Ex-Joyce will then be absorbed by a cold front to be driven into the area by the aforementioned deep-layer cyclone... or alternatively drift south in a fujiwhara interaction with tropical cyclone Kirk to the southeast and be absorbed by the northwestern outer circulation of Kirk.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 30)... 35 mph maximum sustained wind tropical depression centered in the central Atlantic at 22.4N-49.3W
IOH 24 Hr Forecast (1200Z Oct 1)... Remnant low centered in the central Atlantic at 23N-49W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT*************************
2-Day Position (1200Z Oct 2)... 25 mph maximum sustained wind dissipating remnant low centered at 27-49W
REMNANTS OF ISAAC... In the open north Atlantic... after tropical cyclone Isaac previously was arcing more north in track while swung by the current northwest Atlantic deep-layer frontal cyclone... the track has recently deviated more eastward while Isaac has been caught in the flow associated with the tail-end of the high-latitude upper trough that has dove southeast into Europe from Greenland. Decreasing sea-surface temps along the track caused Isaac to weaken from a hurricane to a top-end tropical storm on Sunday... and as of 11 AM EDT today caused Isaac to transition into a remnant non-tropical frontal cyclone centered near 45N-30W.
The tail end of the high-latitude upper trough has left behind a small upper vortex positioned just northwest of ex-Isaac whose southeastern divergence zone is helping to maintain it. The next high-latitude upper trough in the westerlies is currently positioned along the east coast of Canada... over the next 72 hours the south part of this upper trough merges with the upper trough associated with the current northwest Atlantic deep-layer frontal cyclone and re-enforces it... while the north part of the upper trough eventually absorbs the small upper vortex northwest of ex-Isaac and takes over supporting it with its eastern divergence zone. As such... as ex-Isaac continues northeast toward the waters between Iceland and the British Isles... surf generated by it is expected to reach the shores of both locations. Albeit it is also possible for ex-Isaac to lose dominance should the upper divergence maximum of the aforementioned 72-hour northern upper trough fragment setup further north such that ex-Isaac ends up being absorbed by a new northern frontal cyclone that would be developing in its place... if this alternative scenario happens then coastal surf would still happen for the British Isles and Iceland... but it would technically be the replacing frontal cyclone that would be responsible instead of ex-Isaac. And for the Azores... coastal surf continues for the next 72 hours... however becoming increasingly less associated with ex-Isaac and more associated with the aforementioned northwestern Atlantic deep-layer frontal cyclone as that frontal cyclone shifts east with time. This is my final statement on Isaac on this blog as it is no longer a tropical entity... and future impacts to land areas from ex-Isaac will be mentioned on the home page bulletins of this site.
TROPICAL STORM KIRK... Rapid tropical cyclone formation has occurred in the eastern tropical Atlantic... with the tropical wave that was previously tagged as area of interest #35 in the previous blog post being upgraded to tropical depression twelve on Sunday... then within recent hours the depression briskly strengthened into Tropical Storm Kirk with 50 mph maximum sustained winds. Forecast track is initially west-northwest around the southwest periphery of the current eastern Atlantic surface ridge... with a gradual north turn into a mid-ocean ridge weakness that will be caused by two frontal cyclones back-to-back... the first being the current northwest Atlantic frontal cyclone as it swings east... followed by a second west Atlantic frontal cyclone that develops with the support of the upper vorticity that ejects from its current eastern US position. A complete north turn by day 5 is expected around the east side of the second frontal cyclone. It is preferable that the forecast track keeps Kirk a marine threat through day 5 rather than a threat to populated land areas... as conditions for its intensification look excellent while tracking over warm 29 deg C waters and while it remains under an expansive area of low shear and upper outflow... and all the global models agree on Kirk becoming a large and powerful open-ocean hurricane. The initial supply of upper outflow comes from the regional tropical upper ridge cell that Kirk is currently sliding under. I do slow the intensification rate between 48 and 72 hours as the southern base of the mid-latitude upper trough that will be shearing apart Joyce shifts east into Kirk's environment and potentially disrupts Kirk's northwestern outflow. Beyond 72 hours the prolonged isolation from high-latitude cold air... combined with Kirk's thunderstorm latent heat release... should cause the disrupting upper vorticity to dissipate... allowing the eastward-shifting mid-latitude upper ridge currently over the western Atlantic to merge with the tropical upper ridge... resulting in a vast area of favorable low shear and upper outflow. After calling for a category 4 hurricane by day 4... I do not show additional intensification through day 5 as it is hard to know this far in advance what the structure of the hurricane will be like... for instance will it be undergoing an eye wall replacement cycle that holds back further intensification... or will it continue to intensify?
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast********
0 Hr Position (1200Z Sep 30)... 50 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 13.5N-34.8W
IOH 24 Hr Forecast (1200Z Oct 1)... 80 mph maximum sustained wind hurricane centered in the eastern tropical Atlantic at 15N-39.5W
IOH 48 Hr Forecast (1200Z Oct 2)... 115 mph maximum sustained wind major hurricane centered in the central tropical Atlantic at 16.5N-43W
IOH 72 Hr Forecast (1200Z Oct 3)... 120 mph maximum sustained wind major hurricane centered in the central tropical Atlantic at 18.5N-46W
IOH 96 Hr Forecast (1200Z Oct 4)... 130 mph maximum sustained wind major hurricane centered in the central Atlantic at 21N-47.5W
IOH 120 Hr Forecast (1200Z Oct 5)... 130 mph maximum sustained wind major hurricane centered in the central Atlantic at 24N-48W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT*************************
Peak Strength (1200Z Oct 4)... 125 mph maximum sustained wind major hurricane centered in the central Atlantic at 20.7N-46.7W
5-Day Position (1200Z Oct 5)... 120 mph maximum sustained wind major hurricane centered in the central Atlantic at 23.5N-48.7W
AREA OF INTEREST #34... A surface tropical wave of low pressure has recently moved into the western Caribbean from the central Caribbean... and based on the latest satellite imagery and CIMSS 850 mb vorticity product as of this writing (https://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=) has a pair of maximum spins... one located just offshore of the Nicaragua/Honduras border and another near the northeastern corner of the Yucatan peninsula. For now the two spins are being handled as one area of interest here and apparently so in the NHC official outlook... however wouldn't be surprised if there was a period of time in future updates where the two are handled separately. Recently the previous wave of upper vorticity that was over the southwestern Caribbean is dissipating over southeastern Mexico... allowing the surface tropical wave to be helped by the outflow of the southwest quadrant of the current west Atlantic deep-layer ridge in addition to split flow upper divergence between the deep-layer ridge and west side of the next wave of upper vorticity currently positioned south of Hispaniola (Haiti and the Dominican Republic). Currently I forecast that for the next 72 hours the two aforementioned surface spins in the surface wave initially undergo a fujiwhara interaction where the two cyclonically orbit each other... with the fujiwhara interaction perhaps further enabled by the cyclonic flow of the next wave of upper vorticity which gets pushed directly into this disturbance by the west Atlantic deep-layer ridge... with the interaction then ending around 72 hours as the two spins most likely merge near the north coast of the Yucatan peninsula. What happens beyond that time largely hinges on the currently developing central Canadian frontal cyclone and its upper trough... with that forecast undergoing some changes each day. The latest forecast shown in the models has the tail end of that upper trough becoming a slow-moving cut-off feature over the south-central United States toward day 5 due to warm core upper ridging prevailing over the United States in the warm sector of the Canadian frontal cyclone... with the remainder of the upper trough becoming a cold core cut-off upper vortex associated with the frontal cyclone's cold sector. The models have backed off in developing this area of interest while now forecasting a broad tropical low that struggles to consolidate into a tropical cyclone. This could be due to the initial state of this area of interest which is already starting off with two maximum spins instead of one... followed by a potentially elongated area of upper divergence in the Gulf of Mexico toward days 4 and 5 (in association with the south-central US upper vorticity) that could cause this system to be elongated with multiple centers instead of circular with a single center. Another factor potentially going against development is possible shear imparted by the forecast south-central US upper vorticity. My current forecast strategy is to drift this system slowly northeast from the north coast of the Yucatan peninsula and into the southeastern Gulf of Mexico on days 4 and 5 in the flow ahead of the upper vorticity... and to agree with the NHC outlook as of this writing which less than 50% peak odds of tropical cyclone formation as the models have backed off in showing development.
Given the current outlook... interests across the Cayman Islands... Yucatan peninsula of Mexico... and western Cuba should watch for possible tropical cyclone impacts (gusty winds... heavy rainfall... and coastal surf) that could arrive by the middle to later part of this week. Even if this system ends up being a complex tropical disturbance with multiple centers... it could still end up produce impacts similar to a tropical cyclone.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 40% (southeastern Gulf of Mexico near 25N-85.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 40%
AREA OF INTEREST #36... The latest tropical wave of low pressure that has emerged into the eastern tropical Atlantic from western Africa so far on satellite pictures has struggled to maintain its independence from strengthening tropical cyclone Kirk located to its immediate west-northwest. However models have ramped up in showing development of this wave... and accordingly the NHC has added the wave into their tropical weather outlook since Sunday. On the one hand tropical cyclone Kirk is expected to dominate the surface inflow in the region. On the other hand the models are currently in unanimous agreement that this wave over the next couple of days gets boosted by split flow upper divergence between the southwest side of the current eastern Atlantic upper vorticity and vast upper anticyclone over Kirk. And by day 5 this tropical wave will be tracking west-northwest into the lower shear environment produced by the southeast side of the vast upper anticyclone. Given the sway in the models showing development... I am also issuing high (above 50%) odds of tropical cyclone formation through day 5... however I am not quiet as high as the latest NHC outlook until this tropical wave indeed shows signs of independence from Kirk.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 70% (eastern tropical Atlantic near 13N-37.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*************************
Formation chance through 48 hours... 50%
Formation chance through 7 days... 90%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 30) CMC Model Run...
**For Tropical Depression Joyce... continues north to 26N-51W through 48 hours while weakening to a remnant low... shortly thereafter loses identity along the surface front driven into this system by the current northwest Atlantic deep-layer cyclone
**For Tropical Storm Kirk... gains hurricane strength and gradually curves north to 34N-46W through 168 hours
**For area of interest #34... current western Caribbean tropical wave develops into a broad tropical low centered just northwest of the Yucatan peninsula by 126 hours... tropical low drifts northeast to 26N-89W through 168 hours
**For area of interest #36... tropical cyclone formation suggested near 10.5N-32.5W at 66 hours... while gaining hurricane strength continues west-northwest to 15.5N-42.5W through 168 hours
0000Z (Sep 30) ECMWF Model Run...
**For Tropical Depression Joyce... becomes quasi-stationary while weakening to a remnant low in the next 24 hours... absorbed into the northwestern outer circulation of Kirk through 66 hours
**For Tropical Storm Kirk... gains hurricane strength and gradually curves north to 35N-46.5W through 168 hours
**For area of interest #34... current western Caribbean tropical wave develops into a broad central Gulf of Mexico tropical low through 150 hours... the broad Gulf of Mexico tropical low begins to drift east by 168 hours
**For area of interest #36... tropical cyclone formation suggested near 11.2N-34W by 114 hours... while gaining hurricane strength continues west-northwest to 15.5N-41W through 168 hours
1200Z (Sep 30) GFS Model Run...
**For Tropical Depression Joyce... continues north to 25N-50W through 33 hours while weakening to a remnant low... while the remnant low continues north-northeast it loses identity shortly thereafter along the surface front driven into remnant low by the current northwest Atlantic deep-layer cyclone
**For Tropical Storm Kirk... gains hurricane strength and gradually curves north to 35N-42W through 168 hours
**For area of interest #34... current western Caribbean wave develops into a compact tropical low centered just offshore of the Nicaragua/Honduras border by 42 hours... the tropical low then continues north-northwest into the Yucatan channel (between the western tip of Cuba and the Yucatan peninsula) through 99 hours without development shown... the tropical low continues north-northwest into the Gulf of Mexico waters south of Louisiana through 168 hours while devolving into a broad feature with multiple centers.
**For area of interest #36... tropical cyclone formation suggested near 11.2N-36.2W at 54 hours... while gaining hurricane strength continues west-northwest to 16.2N-38.8W through 168 hours
1200Z (Sep 30) NAVGEM Model Run...
**Not available at above-mentioned source
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