*******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 11 2024 11:59 PM EDT...
The surface and upper air charts valid for the time of the initial release of this update are now included below.
...FRIDAY OCTOBER 11 2024 4:50 PM EDT...
Tropical cyclones Leslie and Milton have undergone rapid collapses over the last 48 hours... see remnants of Milton and Tropical Storm Leslie section below for details. Elsewhere monitoring the following areas of interest:
(1) A tropical wave of low pressure currently producing vigorous weather across the Republic of Cabo Verde Islands which may still develop as it moves across the open eastern and central tropical Atlantic... see area of interest #40 section below for details.
(2) A broad area of low pressure appears to be developing in the central Caribbean and may gradually develop in the days ahead... see area of interest #42 section below for details.
TROPICAL STORM LESLIE... Satellite image of Leslie at peak category 2 hurricane intensity (105 mph maximum sustained winds) on 2350Z October 9:
After rapidly intensifying into a category 2 hurricane peak with 105 mph maximum sustained winds late on October 9 and holding that intensity through early October 10... northerly wind shear associated with the east side of an approaching upper anticyclone/ridge proceeded to push Leslie's thunderstorms south of the center. By 5 PM EDT Leslie quickly lost hurricane strength... and through 11 AM EDT today Leslie has weakened to a 50 mph maximum sustained wind cloud swirl tropical storm now void of thunderstorms. The latest upper-level wind analysis shows Leslie is still on the east side of the upper anticyclone instead of the core of the anticyclone where shear would otherwise be lower... therefore time for re-intensification before Leslie interacts with the approaching cold front to the northwest has ran out. The deep-layer westerly flow ahead of the fast-approaching cold front and associated upper trough now departing eastern Canada will accelerate Leslie north... then increasingly northeast then east-northeast through 48 hours. My updated short-term track forecast is quiet similar to the previous as the previous has performed well and the latest model data shows no reason to shift it. Regarding storm structure and strength... it is a close call as to whether or not Leslie will merge with the cold front or just miss it to the south... in the model summary section below the ECMWF does not merge Leslie with the front while the CMC and GFS do so. My current forecast assumes Leslie weakens to a tropical depression soon due to the ongoing lack of thunderstorms in the circulation... then by 24 hours hang on as a tropical depression while encountering supportive split flow upper divergence between westerlies on the north side of the upper anticyclone and the southwesterly flow ahead of the approaching upper trough from eastern Canada which may allow Leslie to re-develop thunderstorms. By 48 hours I then forecast Leslie to merge with the front and hence lose tropical characteristics... however I also expect Leslie to re-intensify but as a frontal cyclone due to the aforementioned split flow upper divergence. If Leslie somehow manages to stay just south of the front... the combination of split flow upper divergence and rapid east-northeast motion which may help it keep up with the speed of the shearing upper westerlies may allow it to re-intensify as a tropical cyclone. My forecast for now ends at 48 hours with the assumption that Leslie is no longer tropical... however the following are possibilities for Leslie after that time:
(1) Whether Leslie is a non-tropical frontal cyclone along the cold front or a tropical cyclone just south of the front... between 48 and 72 hours Leslie will have more spent time over waters below 26 deg C and should no longer be tropical even if it stays just south of the front. The surface circulation of what would be ex-Leslie by this time will also be weakening as it moves east-southeast away from the Azores and toward the Canary Islands under suppressive upper convergent northwesterly flow on the east side of the mid-ocean upper anticyclone.
(2) Between 72 and 96 hours... there are now some model runs that have the approaching upper trough dig toward ex-Leslie... deflecting ex-Leslie more east into northern Canary Islands and potentially allowing it to re-strengthen with the return of split flow upper divergence between the northeast side of the upper anticyclone and digging-in upper trough to the northwest.
(3) Between 96 and 120 hours... the upper divergence maximum of the upper trough will be north of ex-Leslie where it will continue to generate one or more frontal lows... thus ex-Leslie is likely to lose its identity to the northern frontal low(s) as it moves toward northwestern Africa or southern Portugal in this timeframe.
Regarding impact to land areas... per the above long-term evolution of ex-Leslie shown in the latest model runs... the Azores and Canary Islands are increasingly likely to see gusty winds and coastal surf. The Azores would likely see these weather conditions on Sunday... then the Canary Islands by early next week.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Oct 11)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 26.4N-50W
IOH 24 Hr Forecast (1200Z Oct 12)... 35 mph maximum sustained wind tropical depression centered in the central Atlantic at 32N-45W
IOH 48 Hr Forecast (1200Z Oct 13)... Remnant frontal cyclone centered west-southwest of the Azores at 35.5N-34W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT*************************
3-Day Position (1200Z Oct 14)... 35 mph maximum sustained wind dissipating frontal low centered just southeast of the Azores at 36.4N-24.6W
REMNANTS OF MILTON... Satellite imagery of Hurricane Milton as it crossed the Florida peninsula... left is during the landfall on the west coast of Florida late on Wednesday October 9... right is Milton during its rapid transition into a non-tropical remnant frontal cyclone offshore of the Florida east coast on October 10:
Previous post #97 (https://www.infohurricanes.com/post/my-2024-atlantic-hurricane-season-birdseye-view-post-97) documents Milton's rapid eastward passage across the Florida peninsula and into the western Atlantic waters between the Bahamas and Bermuda... and also documents Milton's rapid transition from major hurricane intensity and into a remnant non-tropical frontal cyclone. A sample of wind measurements seen across the Florida peninsula and Keys during Milton's passage is in the table below. Ex-Milton will continue east into the waters just south of Bermuda... then into the open central Atlantic... in the deep-layer westerly flow produced by the combination of the upper westerly jet between the mid-ocean upper anticyclone and upper trough now moving offshore from eastern Canada and the surface westerlies south of the Atlantic Canada frontal cyclone. Ex-Milton will continue to fade in strength as the upper trough and westerly jet lift northeast and leave behind ex-Milton... reducing the supporting upper divergence over ex-Milton caused by the winds accelerating into the westerly jet. However ex-Milton will remain vigorous enough through 24 hours to produce surf reaching the shores of Bermuda. In the long range... warm surface southerly flow ahead of the next frontal cyclone that moves into Atlantic Canada by days 4 and 5 (not to be confused with current Atlantic Canada frontal cyclone) will help lift a portion of the mid-ocean warm core upper anticyclone/ridge north toward the open central Atlantic which would regional wind shear and potentially increase regional upper outflow. Therefore assuming ex-Milton is still around in the open central Atlantic by that time... may have to watch for its possible redevelopment into a tropical cyclone. For now this is my planned final statement on Milton as it is no longer a tropical system... and will re-introduce the remnants of Milton as an area of interest for tropical re-development if necessary in future updates.
The following are the strongest winds (in mph) produced by Milton that were recorded at each of the following National Weather Service stations (weather.gov):
**Tampa (west-central FL)... sustained 52... gust 85... 10:53 PM EDT Oct 9
**Bradenton (west-central FL)... sustained 53... gust 93... 7:53 PM EDT Oct 9
**Punta Gorda (southwestern FL)... sustained 51... gust 79... 7:53 PM EDT Oct 9
**Fort Myers (southwestern FL)... sustained 22... gust 43... 1:53 PM EDT Oct 9
**Naples (southwestern FL)... sustained 28... gust 58... 4:53 PM EDT Oct 9
**Key West (western FL Keys)... sustained 31... gust 55... 11:53 AM EDT Oct 9
**Marathon (central FL Keys)... sustained 20... gust 41... 2:53 PM EDT Oct 9
**Miami (southeast FL)... sustained 28... gust 40... 5:53 PM EDT Oct 9
**West Palm Beach (southeast FL)... sustained 32... gust 60... 4:53 AM EDT Oct 10
**Okeechobee (inland southeast FL)... sustained 37... gust 69... 12:15 AM EDT Oct 10
**Fort Pierce (southeast FL)... sustained 35... gust 68... 2:53 AM EDT Oct 10
**Melbourne (east-central FL)... sustained 43... gust 78... 6:53 AM EDT Oct 10
**Daytona Beach (northeast FL)... sustained 44... gust 83... 4:53 AM EDT Oct 10
**Orlando (central FL)... sustained 37... gust 71... 4:53 AM EDT Oct 10
**Ocala (north-central FL)... sustained 24... gust 38... 11:51 PM EDT Oct 9
**Gainesville (north-central FL)... sustained 28... gust 44... 1:53 AM EDT Oct 10
**Perry (northwest FL)... sustained 17... gust 40... 10:35 PM EDT Oct 9
**Jacksonville (northeast FL)... sustained 29... gust 40... 3:56 AM EDT Oct 10
AREA OF INTEREST #40... The lowest pressures of the eastern Atlantic tropical wave has spent much of today crossing the southern Republic of Cabo Verde Islands... and the islands have experienced periods of heavy rainfall and gusty winds. Observations in the islands showed winds of tropical storm force... however according to recent NHC tropical weather outlooks a satellite scan of winds showed the surface circulation was too elongated north-south (without a well-defined center) to declare a tropical storm. Going forward... surface ridging is expected to regain footing in the central Atlantic through day 5 underneath the western convergence zone of the current eastern Atlantic upper trough as it departs... followed by the eastern convergence zone of the current upper anticyclone/ridge moving into the mid-ocean... then followed by the western convergence zone of the current eastern Canada upper trough when it later moves across the Atlantic. The central Atlantic surface ridging will help push the tropical wave west away from the Republic of Cabo Verde Islands in the short-term... and into the open central tropical Atlantic in the long-term. Currently upper-level conditions for development have remained favorable for development as the west Africa coastal upper vorticity has stayed away from the tropical wave so far... however through day 3 the upper vorticity is expected to chase the tropical wave while pushed by the mid-ocean upper anticyclone. On the one hand divergence between the west side of the upper vorticity and south side of the mid-ocean upper anticyclone could aid the wave's thunderstorm activity... on the other hand the west side of the upper vorticity could induce unfavorable northeasterly shear over the surface wave. And if future model runs show the upper vorticity moving just a little faster... it could overtop the surface wave and ultimately suppress it upper outflow and development potential. Given the uncertainty regarding the upper-level wind outlook through day 3... I continue to assign a low 20% odds of tropical cyclone formation for this timeframe. By days 4 and 5 the chasing upper vorticity fades from its prolonged isolation from high-latitude cold air... allowing the mid-ocean upper anticyclone featuring low shear and upper outflow to increasingly take over. Thus I assign a higher 40% chance of tropical cyclone formation toward day 5.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 3 days... 20% (eastern tropical Atlantic near 15N-38.5W)
Formation chance days 3 to 5... 40% (central tropical Atlantic near 15N-45W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*************************
Formation chance through 48 hours... 50%
Formation chance through 7 days... 50%
AREA OF INTEREST #42... For the Caribbean Sea... ex-Milton has driven the tail end of a decaying cold front/surface trough into the northwestern Caribbean... and surface pressures have dropped along with a corresponding increase in rotating thunderstorms in the southern Caribbean to the east of Central America due to split flow upper divergence between the west side of upper vorticity that has recently retrograded southwestward across the southern Caribbean from the central Atlantic and the south side of the sprawling mid-ocean upper anticyclone/ridge. Over the next 48 hours the upper vorticity continues retrograding westward across the southern Caribbean while the northwest Caribbean surface trough and southern Caribbean surface low pressure field potentially merge into a broad tropical low... however the upper vorticity is likely to cap tropical development during this time. In the 3 to 5 day window... upper winds become more conducive for the development of the central Caribbean broad tropical low as the upper vorticity fades from prolonged isolation from high-latitude cold air... and as the southwestern lobe of the mid-ocean upper anticyclone (featuring outflow and low shear) continues to hang over the central and western Caribbean. Noting that the next Atlantic Canada frontal cyclone (not to be confused with the current one) is expected to be in place by days 4 and 5... with the surface cold front driven by the cyclone advancing toward the central Caribbean and potentially adding to its thunderstorms and surface low pressure field. Some models develop the broad central Caribbean tropical low into a tropical cyclone in 5+ days... particularly the GFS. For this update... I assign a 30% chance of tropical cyclone formation toward day 5 as not all models currently agree on development. Noting that beyond day 5 a deep-layer ridge is likely to build over the eastern US in the wake of the day-5 Atlantic Canada frontal cyclone... this signal points to a westward push of this system by the deep-layer ridge and toward Central America in the long range. As such... interests in Central America should be aware of the possible Caribbean tropical development in the days ahead.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 2 days... 0% (central Caribbean near 15N-80W)
Formation chance days 3 to 5... 30% (central Caribbean near 15N-80W)
*****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 11) CMC Model Run...
****For Tropical Storm Leslie... merges with cold front and becomes a remnant frontal low near 33N-41W at 42 hours... remnant frontal low continues east-northeast into the southeastern Azores through 78 hours and passes just north of the Canary Islands through 108 hours... loses identity shortly thereafter
**For area of interest #40... through 168 gradually weakens to a surface trough that accelerates west-northwest into the waters just north-northeast of the northern Lesser Antilles
**For area of interest #42... no development shown
0000Z (Oct 11) ECMWF Model Run...
**For Tropical Storm Leslie... regains hurricane strength while accelerating east-northeast while located near 35N-37.5W at 54 hours... weakens back to a tropical storm southwest of the Azores by 72 hours then proceeds east-southeast into the northern Canary Islands as a weakening remnant low through 120 hours... dissipates just offshore of Morocco by 144 hours
**For area of interest #40... while remaining a tropical low continues across the tropical Atlantic and reaches 17.5N-57W through 168 hours
**For area of interest #42... no development shown
1200Z (Oct 11) GFS Model Run...
**For Tropical Storm Leslie... gradually merges with cold front and transitions into a remnant frontal low while moving into the waters just southwest of the Azores through 54 hours... remnant low passes just north of the Canary Islands through 93 hours then loses identity shortly thereafter
**For area of interest #40... proceeds west and weakens back to a tropical wave near 15N-44W by 105 hours
**For area of interest #42... through 120 hours the currently developing southern Caribbean low merges with tail end of surface trough that has recently moved into the NW Caribbean while driven by ex-Milton... and also merges with cold front driven into the Caribbean by a days 4 to 5 Atlantic Canada frontal cyclone (not to be confused with current Atlantic Canada frontal cyclone)... tropical cyclone formation suggested near 14.8N-81W through 135 hours and rapidly intensifies into a major hurricane while quasi-stationary at this location through 168 hours
1200Z (Oct 9) NAVGEM Model Run...
**Not available at above-mentioned source
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