*******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.*********
...SUNDAY SEPTEMBER 8 2024 11:59 PM EDT...
The Atlantic tropics remain busy with three concurrent areas of interest… see birdseye view chart above for the current position of each area of interest (as of this writing)… and see the individual area of interest sections below for more information on each one. Also note the following regarding impact to land areas:
(1) Area of interest #19 is expected to bring tropical cyclone impacts to northeast Mexico and all of coastal Texas within the next few days… likely spreading across more inland areas of southeast Texas… and also across Louisiana…. western Mississippi… and Arkansas… please see the area of interest #19 section below for more detailed information including on timing of impacts.
(2) Area of interest #26 may bring impacts to the Republic of Cabo Verde Islands within the next couple of days.
In addition to the current areas of interest… noting the following elsewhere across the Atlantic basin:
(1) The former northwest Atlantic frontal low… tagged as area of interest #24 in previous updates… over the weekend continued across Nova Scotia and was absorbed by the current eastern North America frontal system while moving into Quebec… and did NOT achieve subtropical cyclone status before moving into cooler waters.
(2) The frontal low that formed well southeast of Newfoundland over the weekend has whirled southwest into the northwest side of the regional cut-off upper vorticity… and is not undergoing any tropical development while suppressed by upper convergence on this side of the upper vorticity.
AREA OF INTEREST #19 (POTENTIAL TROPICAL CYCLONE SIX)… The trans-Atlantic and Caribbean tropical wave of low pressure we have been tracking over the last several days… tagged as area of interest #19 on this site… spent Friday and Saturday crossing the Yucatán peninsula of Mexico and entering the eastern Bay of Campeche. As of late the spin of the tropical wave is now merging with the spin of a tropical low of frontal origin that was in the northwest Gulf of Mexico (tagged as area of interest #25 in previous updates) to make a broad low pressure gyre centered near 22.5N-95W as of 1800Z earlier this afternoon. As the regional thunderstorms continue to increase and become better organized… the NHC has upgraded the gyre to potential tropical cyclone six… in order to issue tropical storm advisories ahead of time for northeast Mexico in anticipation this system will become a tropical storm.
The spin of the seedling tropical wave has been kept further east by the northwest Gulf spin it is now absorbing… which should now allow the center of this system to stay just offshore of northeast Mexico and Texas as it curves around the surface ridge currently settling into the eastern US instead of an early landfall and demise over these areas. For the next 24 hours I forecast the two spins to finish merging near 22.5N-95W… then drift west to 96W after the merger is completed while pushed by the aforementioned surface ridge (this initial west move is why my forecast track tends to be west of this past 1200Z GFS model run). After 24 hours the surface ridge shifts east and an upper trough/surface frontal system slowly approaches from the western US… with the steering flow between these features causing this system to recurve north then northeast just offshore of northeast Mexico and Texas. Upper vorticity currently over the southwest US is also forecast to reach this system sooner than the larger-scale western US system… and this upper vorticity should also help with the north and northeast turn. The best window for intensification is between 24 and 48 hours... after this system develops a better-defined center and before shear increases from the incoming southwestern US upper vorticity. Overall I agree with the current NHC intensity forecast which keeps the peak intensity no higher than a category 1 hurricane due to the expected increase in shear before landfall... and because the forecast track is so close to the northeast Mexico and Texas shoreline that any future shifts in the track could increase unfavorable land interaction. Between 72 and 96 hours I forecast a landfall either over or just west of the Texas/Louisiana border. 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. Increasing divergence on the east side of the possible upper vortex could slow the weakening rate of this system after landfall... and my 96-hour forecast point still calls for storm-force strength despite several hours over land. Although the surface cold front of the approaching western US frontal system does not yet reach this system by 96 hours... I still forecast this system to no longer be tropical by 96 hours as it loses thunderstorms while ingesting dry sinking air associated with the western convergence zone of the possible upper vortex... hence I end my forecast for this system at that time.
Interests along coastal Tamaulipas (northeastern Mexico) and coastal southern Texas should now preparing for gusty winds... heavy rainfall with flash flooding potential... and storm force winds with some damage potential arriving by Tuesday. Interests across southeastern Texas and southwestern Louisiana (both near the coast and inland) should be aware that similar conditions... with possible hurricane-force winds... appear likely to arrive by Wednesday. The remainder of Louisiana... western Mississippi... and Arkansas should be watching for possible tropical storm conditions (gusty winds... heavy rain... and coastal surf) from this system arriving by late Wednesday to Thursday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Sep 8)… 50 mph maximum sustained wind tropical low centered in the western Gulf of Mexico at 21.6N-94.6W
IOH 24 Hr Forecast (1800Z Sep 9)… 50 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 22.5N-96W
IOH 48 Hr Forecast (1800Z Sep 10)… 70 mph maximum sustained wind tropical storm centered just offshore of Tamaulipas at 24.5N-97.5W
IOH 72 Hr Forecast (1800Z Sep 11)… 80 mph maximum sustained wind hurricane centered just southeast of Matagorda Bay Texas at 27.5N-96W
IOH 96 Hr Forecast (1800Z Sep 12)… 45 mph maximum sustained wind surface low centered over east-central Arkansas at 35N-91.8W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 PM EDT*************************
Landfall (0000Z Sep 12)... 80 mph maximum sustained wind hurricane centered over the southwestern corner of Louisiana at 29.9N-93.1W
5-Day Position (0000Z Sep 14)... 25 mph maximum sustained wind remnant low centered over the southern Missouri/Illinois border at 37.3N-89.5W
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 90%
Formation chance through 7 days... 90%
AREA OF INTEREST #23... The tropical wave of low pressure that was in the eastern Atlantic over the last couple of days has continued westward to 12.5N-42.5W (central tropical Atlantic)... where it has developed a well-defined spin with thunderstorms. Albeit the most recent satellite frames have shown the thunderstorms have dwindled perhaps due to suppression of poleward outflow from adjacent eastern Atlatnic upper vorticity. However the nearby tail of the upper vorticity is forecast to swing east and away with this feature remaining under regional anticyclonic outflow and low shear... therefore remaining on guard that this system has a heightened chance of tropical cyclone formation... especially as it has developed a well-defined spin over the weekend. As far as track... models have come into agreement that over the next 48 hours this system remains quasi-stationary as steering currents have weakened due to the Atlantic surface ridge being eroded by the eastern divergence zone of the aforementioned large-scale eastern Atlantic upper vorticity... however a north drift toward the ridge weakness associated with the current weakening frontal low southeast of Newfoundland is possible. By 72+ hours the Atlantic surface ridge recovers in the eastern Atlantic due to the eastern convergence zone of a forecast warm core North Atlantic upper ridge which will soon develop in the warm sector of the current eastern North America frontal system... with this system forecast to move west-northwest around the southwest side of the recovered ridge and toward a 120-hour weakness to be positioned just east of Bermuda associated with the tail end of the current eastern North America surface cold front. For now upper winds are forecast to remain favorable for tropical development through 120 hours 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 eastern North America frontal system stays off to the north when it moves into the Atlantic. And combined with the fact this system now has a well-defined spin... I agree with the NHC on odds of tropical cyclone formation greater than 50%... however I do not have odds quiet as high as the NHC in case the upper wind forecast toward day 5 changes in future updates (for instance many of the model runs early Sunday did not develop this system... perhaps an indication that there is also still some chance that some disrupting upper vorticity may be in this system's environment in the longer range).
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 60% (northeast of the northern Lesser Antilles near 20N-57.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 60%
Formation chance through 7 days... 70%
AREA OF INTEREST #26... On Friday and Saturday it appeared that part of the tropical wave of low pressure that was over Western Africa became entangled with the current upper vortex system over Western Europe while moving into northwest Africa… while the other part of the wave continued into the eastern tropical Atlantic and contributed to a recent surface trough of low pressure generally south of the Republic of Cabo Verde Islands. The outflow of the regional tropical upper ridge axis may have also contributed to the materialization of the offshore surface trough. Also noting another tropical wave of low pressure has spent the last couple of days moving from central Africa to Western Africa… and is expected to move into the eastern tropical Atlantic and merge with the offshore surface trough within the next couple of days. Then by 72+ hours the Atlantic surface ridge recovers in the eastern Atlantic as noted in the above area of interest #23 section… sending the surface trough west toward the central tropical Atlantic through day 5. My 30% peak odds of tropical cyclone formation are currently below the NHC as its possible the elongated surface trough struggles to develop a well-defined center needed for cyclone formation… or ends up having multiple centers that compete with each other. Also a surge of disrupting dry Saharan air may be sent into the eastern tropical Atlantic when the eastern Atlantic surface ridge recovers in a few days.
So far the inclement weather associated with the surface trough has stayed south of the Republic of Cabo Verde Islands… however over the next couple of days will watch to see if the current Western Africa tropical wave brings heavy rain and gusty winds to the islands when it moves offshore and merges with the surface trough.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 30% (eastern tropical Atlantic near 14N-39W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 60%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 8) CMC Model Run...
**For area of interest #19 currently in the western Gulf of Mexico… tropical cyclone formation suggested at 22N-96W at 54 hours… while strengthening and moving north the center of the cyclone reaches waters just offshore of south Texas by 84 hours then curves northeast for a landfall near Galveston Bay Texas by 102 hours… continues north-northeast into Ohio Valley & Great Lakes region of US thru 168 hours while transitioning into a remnant frontal low
**For area of interest #23 currently in the central tropical Atlantic… drifts slowly north as a tropical low through 66 hours after which time it turns west-northwest while degenerating back to a wave
**For area of interest #26 (surface trough currently in the eastern tropical Atlantic)… merges with additional tropical wave that emerges from west coast of Africa at 42 hours… northeast end of surface trough then becomes tropical low over Republic of Cabo Verde Islands by 66 hours and then a possible weak tropical cyclone near 17.5N-33W by 96 hours… the possible weak tropical cyclone reaches 19.5N-45.5W through 168 hours
**Tail end of current eastern North America frontal system becomes a cut-off frontal low just northeast of Bermuda at 138 hours… strengthens into a surface cyclone with possible tropical characteristics through 168 hours while reaching 37N-58W
0000Z (Sep 8) ECMWF Model Run...
**For area of interest #19 currently in the western Gulf of Mexico… possible weak tropical cyclone formation suggested at 22N-96W at 60 hours… while only gradually strengthening and moving north the center of the cyclone reaches waters just offshore of south Texas by 90 hours then curves northeast for a landfall near the TX/LA border by 108 hours… continues north-northeast into Ohio Valley region of US thru 168 hours while transitioning into a remnant frontal low
**For area of interest #23 currently in the central tropical Atlantic… drifts slowly north as a tropical low through 60 hours after which time it turns west while degenerating back to a wave
**For area of interest #26 (surface trough currently in the eastern tropical Atlantic)… west end of surface trough develops into a tropical cyclone near 11.2N-34.5W at 72 hours… moves west-northwest to 20N-46W thru 168 hours while becoming a hurricane
1200Z (Sep 8) GFS Model Run...
**For area of interest #19 currently in the western Gulf of Mexico… tropical cyclone formation shown just offshore of the Tamaulipas/Veracruz border at 30 hours… subsequently becomes a potentially strong hurricane that continues north-northeast into southwestern Louisiana through 84 hours… subsequently drifts north-northeast into northeast corner of Arkansas through 144 hours where it fades into a dissipating inland remnant low.
**For area of interest #23 currently in the central tropical Atlantic… drifts slowly north as a tropical low through 60 hours after which time it turns west-northwest while degenerating back to a wave
**For area of interest #26 (surface trough currently in the eastern tropical Atlantic)… merges with additional tropical wave that emerges from west coast of Africa at 36 hours… thru 75 hours the surface trough develops two low pressure centers with an ENE center over the Republic of Cabo Verde Islands and WSW center near 10.5N-36W… both centers gradually merge in the central tropical Atlantic through 114 hours… thru 168 hours the SW end of the merged circulation consolidates into a circular tropical low near 15.5N-46W
0600Z (Sep 8) NAVGEM Model Run...
**For area of interest #19 currently in the western Gulf of Mexico… tropical cyclone formation shown near 22N-96W at 36 hours… subsequently becomes a potentially strong hurricane that continues north-northeast into the TX/LA border through 84 hours… continues north-northeast into Ohio Valley & Great Lakes region of US thru 150 hours while transitioning into a remnant frontal low… remnant frontal low loses identity to large frontal system to the west thereafter
**For area of interest #23 currently in the central tropical Atlantic… quasi-stationary through 48 hours as a tropical low after which time it turns west-northwest and reaches 20.9N-61.5W through 168 hours (potentially a weak tropical cyclone through that time)
**For area of interest #26 (surface trough currently in the eastern tropical Atlantic)… consolidates into a tropical low near 15.5N-41W at 126 hours… while strengthening into a tropical cyclone continues west to 16N-49W through 168 hours
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