*******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 SEPTEMBER 13 2024 6:55 AM EDT...
The surface and upper air charts valid for September 11 are added to this post... they were not intially generated and included to ensure a more timely release of the update.
Francine is now a post-landfall inland remnant low centered over northeastern Arkansas bringing heavy rainfall with flash flooding potential to surrounding areas. The western of the two tropical lows in the central Atlantic... tagged as area of interest #27 in this blog post... could bring heavy rain and gusty winds to the northern Lesser Antilles today. Tropical Depression Seven has not strengthened into a tropical storm so far... and the next update will have a lowered intensity forecast relative to what I showed in the full update below.
...WEDNESDAY SEPTEMBER 11 2024 11:15 PM EDT...
The Atlantic tropics remain rather busy with landfalling Hurricane Francine in Louisiana... two areas of interest in the central tropical Atlantic... newly-formed tropical depression seven in the eastern tropical Atlantic... and finally yet another area of interest offshore of the southeastern United States... see above graphic for the current position of each system (as of this writing). See the individual area of interest sections below for more information on each system including expected impacts to land areas.
HURRICANE FRANCINE (RECENTLY DOWNGRADED TO TROPICAL STORM FRANCINE)… Visible satellite image showing Francine developing an eye as it approached southern Louisiana earlier today (image taken at 1751Z):
The following forecast discussion for Francine was completed at 1200Z earlier today but was not released until now as I also had to complete forecast discussion for the numerous other concurrent Atlantic tropical systems... since then Francine briefly strengthened to a peak of 100 mph maximum sustained winds just before landfall with southern Louisiana... and as of 11 PM EDT has weakened to a inland tropical storm with 70 mph maximum sustained winds whose center is now crossing the New Orleans metro region:
While in the northwestern Gulf of Mexico... Francine has turned northeastward toward southern Louisiana... with landfall expected later today... while being strong/tall enough to be guided by the flow ahead of the approaching southwestern US upper vorticity. Within the last 36 hours... initially the tropical cyclone struggled to strengthen past 65 mph maximum sustained winds as the upper flow sheared much of the thunderstorms northeast of the cyclone's core. However a small area of thunderstorms remained attached to the core... and subsequently grew in size which helped the tropical storm finally become a category 1 hurricane with 90 mph maximum sustained winds. The growing thunderstorm canopy has been stretched southwest-northeast which indicates the hurricane remains stressed by southwesterly wind shear... therefore additional intensification before landfall with southern Louisiana is not anticipated... albeit for the first time visible satellite pictures (around 1800Z) are showing the formation of an eye so a little more intensification just before landfall is not entirely out of the question. Once again Francine is east of the previous forecast and so the updated one is adjusted accordingly... and calls for a landfall over south-central Louisiana just southwest of the New Orleans Metro region. Noting during landfall the upper vorticity that moves in from the southwest US begins to amplify into a possible upper vortex as adjacent warm core upper ridging amplifies to the north in the warm sector of the slowly-approaching western US frontal system... and after landfall Francine is expected to whirl north then north-northwest into the core of the possible upper vortex. At first reduced shear and increasing upper divergence on the east side of the possible upper vortex may help with a little more pre-landfall intensification... and slow the inland weakening rate of Francine... which is why I forecast storm-force intensity at 24 hours despite the landfall. Then by 48+ hours once Francine stalls beneath the core of the possible upper vortex... where upper divergence is also lacking... the inland remnant circulation is expected to dissipate.
Regarding impacts to land areas:
(1) Due to the ongoing east shifts in the forecast track impacts to coastal Texas will be limited to surf.
(2) Southeastern and south-central Louisiana are expected to see tropical storm to hurricane force winds and coastal surf later today... preparations for Francine here should have been completed by now.
(3) Mississippi... southeastern Arkansas... the southeast corner of Missouri... southwest corner of Kentucky... and western Tennessee may see inland tropical storm force gusts as Francine moves inland through tomorrow. Coastal Alabama may also see coastal surf.
(4) Based on the latest doppler radar presentation (as of this writing)... an area of heavy rainfall associated with Francine's moisture and upper divergence on the east side of the materializing regional upper vortex is currently producing heavy rainfall with flash flooding potential across northwestern Louisiana... south-central and southeastern Louisiana... southern Arkansas... southern Mississippi... and southern Alabama. Expect the rainfall to spread across the remainder of Arkansas... Mississippi... western Alabama... southeastern Missouri... southwestern Kentucky... and western Tennessee as Francine moves inland over the next day or so.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 11)... 90 mph maximum sustained wind hurricane centered offshore of southern Louisiana at 28N-92.7W
IOH 24 Hr Forecast (1200Z Sep 12)... 45 mph maximum sustained wind tropical storm centered over northwestern Mississippi and just east of the Arkansas border at 33.5N-90.5W
IOH 48 Hr Forecast (1200Z Sep 13)... Weakening remnant low centered over Tennessee/Arkansas border at 35.5N-90W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT*************************
Landfall (0000Z Sep 12)... 90 mph maximum sustained wind hurricane centered over the coast of south-central Louisiana at 29.5N-91.5W
60-Hr Position (0000Z Sep 14)... 25 mph maximum sustained wind dissipating remnant low centered over the northeast corner of Arkansas at 35.7N-90.2W
AREA OF INTEREST #23... The central Atlantic tropical low has finally begun to move west under the influence of the recovered eastern Atlantic surface ridge... and it is expected through day 4 to move west-northwest into the western Atlantic waters north of the Caribbean Islands while gravitating toward a ridge weakness associated with a frontal low that will soon develop in the central Atlantic. The ridge weakness then continues with development of area of interest #28 offshore of the southeastern US... and by day 5 I currently forecast a north turn into the weakness. Through day 4 upper winds are forecast to remain favorable for tropical development as the current western Atlantic upper vorticity is forecast to fade fast enough to not disrupt this system while at the same time upper vorticity tied to the current eastern and western Canada upper troughs stays off to the north when those features later move into the Atlantic... and as a result in this update I continue to forecast odds of tropical cyclone formation of 50% which is higher than the NHC outlook as of this writing. By day 5 I lower odds of development to 30% while this system moves into an increased shear environment on the southeast side of the upper vorticity associated with area of interest #28.
Noting the northern Lesser Antilles... Virgin Islands... and Puerto Rico may see coastal surf from this system by this weekend should it remain vigorous in the days ahead.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 4 days... 50% (just north of the northeastern Caribbean Islands)
Formation chance days 4 to 5... 30% (western Atlantic near 25N-65W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 20%
AREA OF INTEREST #26 (RECENTLY UPGRADED TO TROPICAL DEPRESSION SEVEN)... The northeast end of the elongated eastern Atlantic surface trough... which passed over the Republic of Cabo Verde Islands late Tuesday and early today... briskly organized into the seventh tropical depression of the 2024 Atlantic Hurricane Season by 11 AM EDT while moving into the waters west of the islands. The track forecast is steady to the west-northwest into the open central Atlantic Ocean through day 5... toward the ridge weakness of a central Atlantic surface frontal low which will strengthen into a frontal cyclone during the forecast period. Note for the next 24 hours the north angle in the track is also helped by the remainder southwestern portion of the surface trough from which this tropical depression originated within. The track forecast slows down in forward speed by 72 and 96 hours as steering currents weaken due the expansive nature of the forecast central Atlantic frontal cyclone while the cyclone at the same time stays too far north to influence the steering. A northwest Atlantic steering surface ridge begins to recover in the wake of the frontal cyclone by day 5... and I show some slight increase in the forward speed by that time. Regarding intensity... conditions remain generally favorable for development through 24 hours due to sufficiently warmer waters and the combination of the low shear/outflow of the overhead tropical upper ridge axis... and I forecast some gradual development to a tropical storm... the key word being gradual as this system could inhale the band of dry Saharan air to the north. Between 24 and 48 hours I pause strengthening as this system could pass below the south side of some of the current eastern Atlantic upper vorticity which would disrupt the upper outflow of this system. Beyond that time shear and upper outflow disruption ends as this system continues west-northwest below the remainder western portion of the regional tropical upper ridge axis while at the same time reaching warmer waters... and I forecast a ramp-up into a category 2 hurricane through day 5.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Sep 11)... 35 mph maximum sustained wind tropical depression centered in the eastern tropical Atlantic at 16.2N-30.3W
IOH 24 Hr Forecast (1800Z Sep 12)... 50 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 17.5N-35W
IOH 48 Hr Forecast (1800Z Sep 13)... 50 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 18.5N-40W
IOH 72 Hr Forecast (1800Z Sep 14)... 65 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 19.5N-44W
IOH 96 Hr Forecast (1800Z Sep 15)... 80 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 20N-46.5W
IOH 120 Hr Forecast (1800Z Sep 16)... 100 mph maximum sustained wind hurricane centered in the central Atlantic at 21N-49.5W
*****National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT*************************
5-Day Position (1800Z Sep 16)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 20.7N-47W
AREA OF INTEREST #27... Before moving into the eastern Caribbean...the parent tropical wave of low pressure that deposited area of interest (AOI) #23 also deposited yet another tropical low pressure spin west of AOI #23 which has recently been upgraded to a new area of interest in the NHC outlook product... this marks the twenty-seventh tropical Atlantic area of interest tracked on this site this year. Like neighboring AOI #23... this area of interest is also forecast to move west-northwest into the forecast western Atlantic surface ridge weakness in the days ahead. However due to its more west initial position relative to AOI #23... this system is expected to pass very close to the northeastern Caribbean Islands and could in fact pass directly over the islands. I agree with the NHC in setting low 10% odds of tropical cyclone formation as this system appears smaller and weaker relative to the neighboring AOI which will likely dominate the regional surface inflow and upper outflow. After day 3 I no longer expect development from this area of interest as dual competition with AOI #23 to the east and developing AOI #28 to the northwest make development of this area of interest even more difficult.
If by any chance this system remains vigorous in the days ahead... alongside AOI #23 it could generate coastal surf for the northern Lesser Antilles... Virgin Islands... and Puerto Rico as early as Friday. A direct passage over these islands could result in heavy rainfall and/or gusty winds.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 3 days... 10% (just north of Puerto Rico)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 10%
AREA OF INTEREST #28... The tail end of a surface frontal system that has been slowly edging into the Atlantic from eastern North America over the last couple of days is now in the waters offshore of the southeastern United States. In the previous update there was only a whisper that the tail end of the front could evolve into a subtropical or tropical system as the usually less reliable NAVGEM model suggested this idea... and so at the time I did not upgrade the front to a tropical area of interest. Recently the GFS and ECMWF have joined the NAVGEM... and the NHC has upgraded the front to an area of interest... marking the 28th tropical Atlantic area of interest I have tracked on this site this year.
The amplified upper vorticity that passes over inland tropical cyclone Francine by 3+ days is forecast to continue east into the waters offshore of the southeastern United States... with the combo of high divergence and low shear on the east side of the upper vorticity causing the surface front to quickly evolve into a possible subtropical or tropical cyclone. I have already set my 5-day peak odds of subtropical or tropical cyclone formation as high as 40% for this new area of interest due to the increasingly strong agreement among the global models. Note the system would be subtropical if the surface cyclone ends up being supported by a combination of the warm core outflow of the thunderstorms plus the divergence zone of the cool core upper vorticity... and would be considered tropical if most of its support comes from the warm core outflow of the thunderstorms. As far as steering... models agree that the western convergence zone of the current western Canada upper trough... followed by the western convergence zone of a piece of southeastward-ejecting energy that separates from the current upper trough moving into the western US... will support a strong surface ridge in the northwest Atlantic. The combination of the flow on the northeast side of the aforementioned upper vorticity and strong surface ridge would push anything that develops toward the Carolina coast by early next week (after this weekend)... and I recommend interests here should be monitoring the progress of this area of interest.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 3 days... 0% (offshore of the southeastern United States near 30N-74W)
Formation chance days 3 to 5... 40% (offshore of the southeastern United States near 31.5N-74W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 30%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 11) CMC Model Run...
**For Hurricane Francine currently in the northwestern Gulf of Mexico… makes landfall over south-central Louisiana just after 24 hours… inland remnant low dissipates over eastern Arkansas/Missouri border just after 66 hours.
**For area of interest #23 currently in the central tropical Atlantic… no development shown while dissipating near 15.5N-50W at 30 hours
**For area of interest #26 currently just west of the Republic of Cabo Verde Islands… continues west-northwest to 19.5N-46W through 168 hours while staying a broad tropical low without tropical cyclone formation.
**For area of interest #27 currently in the central tropical Atlantic just west of AOI #23... no development shown while dissipating just northeast of the northern Lesser Antilles at 60 hours
**For area of interest #28 (surface front currently offshore of the southeastern US)... surface front becomes a broad surface low near 31N-78W at 102 hours... broad surface low drifts very slowly north into the coastal Carolinas through 168 hours
0000Z (Sep 11) ECMWF Model Run...
**For Hurricane Francine currently in the northwestern Gulf of Mexico… makes landfall over south-central Louisiana at 24 hours… inland remnant surface low moves into Arkansas/Tennessee border through 78 hours where it then becomes quasi-stationary while trapped beneath overhead passing upper vorticity... dissipates at this location by 96 hours
**For area of interest #23 currently in the central tropical Atlantic… no development shown while dissipating near 15N-53.8W at 54 hours
**For area of interest #26 currently just west of the Republic of Cabo Verde Islands… tropical cyclone formation shown through 12 hours and reaches peak strength near 20N-40W at 66 hours... after briefly weakening begins to re-strengthen while reaching 21.2N-51W through 168 hours
**For area of interest #27 currently in the central tropical Atlantic just west of AOI #23... dissipates just east of the northern Lesser Antilles at 42 hours
**For area of interest #28 (surface front currently offshore of the southeastern US)... surface front becomes a broad east-west elongated low near 30N-75W by 102 hours... while developing further into a more circular subtropical to tropical cyclone moves northwest into the central part of the South Carolina coast through 144 hours... weakening inland remnant low then continues northwest into the North Carolina/Tennessee border through 168 hours
0600Z (Sep 11) GFS Model Run...
**For Hurricane Francine currently in the northwestern Gulf of Mexico… makes landfall over south-central Louisiana at 18 hours… inland remnant surface low moves into Arkansas/Tennessee border through 66 hours where it then becomes quasi-stationary while trapped beneath overhead passing upper vorticity... dissipates at this location by 84 hours
**For area of interest #23 currently in the central tropical Atlantic… no development shown while dissipating near 15N-54.5W just after 48 hours.
**For area of interest #26 currently just west of the Republic of Cabo Verde Islands… the elongated surface trough gradually consolidates into a broad tropical low near 18.5N-39.5W at 63 hours... broad tropical low continues west-northwest to 22N-44.5W through 168 hours without tropical cyclone formation
**For area of interest #27 currently in the central tropical Atlantic just west of AOI #23... dissipates near 15N-56W just after 27 hours
**For area of interest #28 (surface front currently offshore of the southeastern US)... surface front becomes a surface low near 30N-76.2W at 72 hours and while generally quasi-stationary in this region becomes a subtropical or tropical cyclone through 105 hours which wobbles northwest into the North Carolina coast between Cape Fear and Cape Lookout through 144 hours while strengthening further into a hurricane... inland weakening remnant low swings west into the North Carolina/Tennessee border through 168 hours
**A portion of the surface front tied to area of interest #28 also develops into a small surface low near 30N-58.5W at 138 hours... while in fujiwhara interaction with AOI #26 approaching from southeast the surface low drifts south to 28N-58.8W through 168 hours (however tropical development would be difficult due to forecast westerly shear imparted by the southwest side of the upper trough currently over western Canada when that trough later dives southeast into the Atlantic)
0600Z (Sep 11) NAVGEM Model Run...
**For Hurricane Francine currently in the northwestern Gulf of Mexico… makes landfall over south-central Louisiana just after 18 hours… inland remnant surface low moves into eastern Arkansas/Missouri border through 78 hours where it then becomes quasi-stationary while trapped beneath overhead passing upper vorticity... dissipates at this location by 84 hours
**For area of interest #23 currently in the central tropical Atlantic… no development shown
**For area of interest #26 currently just west of the Republic of Cabo Verde Islands… the elongated surface trough gradually consolidates into a broad tropical low near 15.5N-42W through 60 hours... broad tropical low continues west to 17.5N-54W through 168 hours without tropical cyclone formation
**For area of interest #27 currently in the central tropical Atlantic just west of AOI #23... moves west-northwest across the northern Lesser Antilles around 60 hours after which time it loses definition to area of interest #28 developing to the northwest
**For area of interest #28 (surface front currently offshore of the southeastern US)... surface front becomes a surface low near 31N-76.5W at 66 hours and through 90 hours proceeds to become elongated east-west... west end of elongated surface low proceeds to evolve into a tropical or subtropical cyclone near 31.5N-77W through 108 hours... cyclone proceeds to turn north-northeast while gradually strengthening with center reaching waters just offshore of the North Carolina through 144 hours... the center of the cyclone proceeds to arc north-northwest into southern New Jersey through 168 hours.
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