*******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...WEDNESDAY SEPTEMBER 11 2024 10:00 AM EDT...
In the northwestern Gulf of Mexico... Tropical Storm Francine within the last 24 hours has strengthened into a category 1 hurricane with 90 mph maximum sustained winds. The hurricane is tracking further east and landfall is expected over south-central Louisiana instead of southwestern Louisiana. The east shift in the track means impacts to coastal Texas will simply be limited in the form of coastal surf... and coastal surf will now also be possible as far east as Alabama in addition to Louisiana and Mississippi. Interests in southern Louisiana should be rushing preparations to completion for hurricane-force coastal surf... wind... and heavy rainfall with flash flooding potential as weather conditions will deteriorate later today. See Francine section below for impacts also expected in other regions surrounding southern Louisiana.
In the eastern tropical Atlantic... the northeast end of the surface trough of low pressure tagged as area of interest #26 in this post passed over the Republic of Cabo Verde Islands while becoming increasingly organized... and tropical cyclone formation now appears to be occurring just west of the islands. At 9:45 AM EDT the NHC released a special tropical weather outlook bumping up its odds of tropical cyclone formation to 90%.
...TUESDAY SEPTEMBER 10 2024 3:30 AM EDT...
The Atlantic tropics remain busy with newly formed Tropical Storm Francine in the western Gulf of Mexico and two other area of interest in the central and eastern tropical Atlantic… see birdseye view chart above 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 (the most pressing current situation involves Francine which will bring tropical cyclone impacts to northeast Mexico and all of coastal Texas within the next couple of days… likely spreading across more inland areas of southeast Texas… and also across Louisiana…. Mississippi… southeast Arkansas… western Tennessee… southeast corner of Missouri… and southwest corner of Kentucky)
TROPICAL STORM FRANCINE… Satellite imagery of Potential Tropical Cyclone Six becoming Tropical Storm Francine on Monday September 9... left image is when the potential tropical cyclone fired a large thunderstorm mass that caused it to consolidate into Tropical Storm Francine on Monday morning... right image is Francine by Monday evening while it intensified into 65 mph maximum sustained winds:
Potential tropical cyclone six in the western Gulf of Mexico became Tropical Storm Francine on Monday morning as it fired a large thunderstorm mass that helped it develop a well-defined surface low pressure center instead of the previous structure it had over the weekend which was the merger of two centers. The thunderstorm mass has since dwindled... however Francine has developed more mature thunderstorm banding features as it continued to strengthen further to 65 mph maximum sustained winds later on Monday. The tropical storm has moved north-northwest into the waters offshore of northeastern Mexico... and is currently positioned north-northeast of my previous forecast track line and so my updated one is adjusted accordingly. Over the next 24 hours the flow in between the eastward-shifting eastern US surface ridge and out ahead of the slowly approaching western US upper trough/surface frontal system should cause Francine to curve increasingly north into the waters offshore of south Texas... followed by a northeast kick into a landfall with the northwestern US Gulf coast between 24 and 48 hours due to the southwesterly upper flow ahead of the currently approaching southwestern US upper vorticity which should help steer Francine as the tropical cyclone now has a stronger/taller structure. The model guidance has shifted east and calls for the center to make landfall on Louisiana instead of southeast Texas... and with the current position of the storm north-northeast of the previous forecast track line my updated track is also shifted east and now calls for a landfall over southwestern Louisiana in between 24 and 48 hours... with the center of the storm being over interior south-central Louisiana at 48 hours. Because Francine has been strengthening earlier than previously shown... the NHC has continuously been raising the intensity forecast and as of 11 PM EDT called for a category 2 hurricane for peak strength. My intensity forecast still calls for a peak no higher than a category 1 hurricane as Francine has recently stopped strengthening while the tropical storm’s circulation appears to becoming increasingly stretched southwest-to-northeast… an indication that the north adjustment in the track is placing Francine into westerly shearing upper winds on the north side of the Gulf of Mexico upper ridge and out ahead of the approaching SW US upper vorticity sooner. 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 72-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 Francine by 72 hours... I still forecast this system to no longer be tropical 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 Francine at that time.
Regarding impacts to land areas:
(1) Interests along coastal Tamaulipas (northeastern Mexico) and coastal southern Texas should have finished preparing for tropical storm conditions (heavy rainfall with flash flooding potential... coastal surf… and gusty winds) as the core of the tropical cyclone is now just offshore of these locations.
(2) For coastal and inland southeast Texas… tropical storm preparations should be completed by late today as the worst weather arrives by Wednesday… it appears the risk of hurricane force winds in this region has dropped with the latest forecast track shift.
(3) For Louisiana… the southern part of the state should be preparing for hurricane force coastal surf and wind… along with heavy rainfall with flash flooding potential… to arrive by the later part of Wednesday. The northern part of the state will also see inland tropical storm force winds during this time.
(4) For Mississippi… southeastern Arkansas… the southeast corner of Missouri… the southwest corner of Kentucky… and and western Tennessee… if the current forecast track holds inland tropical storm conditions (heavy rain and gusty winds) are expected to spread in by late Wednesday and into Thursday. Coastal Mississippi may also see surf generated by Francine by late Wednesday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 10)… 65 mph maximum sustained wind tropical storm centered offshore of Tamaulipas at 24.1N-96W
IOH 24 Hr Forecast (0000Z Sep 11)… 80 mph maximum sustained wind hurricane centered offshore of southern Texas at 26.5N-96.2W
IOH 48 Hr Forecast (0000Z Sep 12)… 70 mph maximum sustained wind tropical storm centered over inland south-central Louisiana at 30.5N-92.5W
IOH 72 Hr Forecast (0000Z Sep 13)… 40 mph maximum sustained wind surface low centered over northeast corner of Arkansas at 35.8N-90.5W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 PM EDT*************************
Peak Strength (1200Z Sep 11)... 100 mph maximum sustained wind hurricane centered offshore of southwestern Louisiana at 27.9N-93.7W
Landfall (0000Z Sep 12)... 85 mph maximum sustained wind hurricane centered over the coast of south-central Louisiana at 29.9N-92.2W
4-Day Position (0000Z Sep 14)... 25 mph maximum sustained wind dissipating remnant low centered over the southeast corner of Missouri at 36.6N-90W
AREA OF INTEREST #23... The central Atlantic tropical low has been meandering in weak steering over the last 24 hours while drifting northeast to 15N-41W. The tropical low has been struggling to develop thunderstorms perhaps while in competition for surface inflow with adjacent area of interest #26 to its east and the NHC has dropped odds of tropical cyclone formation in its recent outlooks. However given the most recent satellite frames which show thunderstorms redeveloping… I chose to only lower my odds of tropical cyclone formation to 50%. As far as track... models have come into agreement that steering currents will soon recover as the Atlantic surface ridge recovers in the eastern Atlantic due to the eastern convergence zone of the currently developing warm core North Atlantic upper ridge... with this system forecast to move west-northwest around the southwest side of the recovered ridge and toward a day 4 weakness to be positioned just east of Bermuda in association with the tail end of the current western Atlantic cold front… where another frontal low is forecast to develop. However a total turn to the north is not forecast through day 5 as the surface ridge weakness is expected to be narrow. 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 upper trough and current western Canada upper trough stays off to the north when those features later move into the Atlantic. Noting I do not have odds of cyclone formation higher than 50% in case the upper wind forecast toward day 5 changes in future updates (for instance many of the model runs still do 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).
Noting the northern Lesser Antilles… Virgin Islands… and Puerto Rico may see coastal surf from this system by this weekend should it remain vigorous thru day 5 while passing just north of these islands.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 50% (just north of the northeastern Caribbean Islands)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************
Formation chance through 48 hours... 40%
Formation chance through 7 days... 40%
AREA OF INTEREST #26... A tropical wave of low pressure currently emerging from the west coast of Africa is merging with a pre-existing offshore surface trough of low pressure south of the Republic of Cabo Verde Islands… watching to see if this disturbance later consolidates and undergoes tropical development in the days ahead. The currently elongated surface trough is expected to move west then west-northwest in the same steering to guide adjacent area of interest #23 to the west. My 30% peak odds of tropical cyclone formation remain 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 steering eastern Atlantic surface ridge recovers soon… and around day 5 some model runs indicate that that some of the current east Atlantic upper vorticity could retrograde southwest overtop this system which could disrupt it. Noting that regardless of tropical cyclone formation or not… the northeast end of the surface trough which contains the tropical wave just offshore of Africa could bring some periods of rainfall and gusty winds within the next couple of days.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 30% (eastern tropical Atlantic near 17N-41W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************
Formation chance through 48 hours... 30%
Formation chance through 7 days... 70%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
1200Z (Sep 9) CMC Model Run...
**For Tropical Storm Francine… makes landfall over south-central Louisiana just before 72 hours… continues north-northeast then north-northwest into and along Missouri/Illinois border through 108 hours while an inland weakening remnant low… through 150 hours the remnant low curves north-northeast across Wisconsin and Upper Peninsula of Michigan after which time it loses identity to large frontal low moving across Canada.
**For area of interest #23… quasi-stationary through 24 hours after which time it turns west-northwest while degenerating back to a wave
**For area of interest #26… eventually consolidates into a single tropical low that reaches 20N-41W through 168 hours while possibly being a weak tropical cyclone for a period of that time
1200Z (Sep 9) ECMWF Model Run...
**For Tropical Storm Francine…makes landfall over south-central Louisiana just before 66 hours at hurricane strength… the inland remnant low then dissipates over the northeast corner of Arkansas after 126 hours
**For area of interest #23… quasi-stationary through 24 hours after which time it turns west while degenerating back to a wave
**For area of interest #26… consolidates into a single tropical low near 17N-39W by 84 hours with tropical cyclone formation suggested near 19.5N-48.5W by 138 hours… while gradually strengthening the tropical cyclone reaches 20.2N-52W through 168 hours
1800Z (Sep 9) GFS Model Run...
**For Tropical Storm Francine…makes landfall over south-central Louisiana at 54 hours at hurricane strength… the inland remnant low then dissipates over far western Tennessee after 108 hours
**For area of interest #23… quasi-stationary through 24 hours after which time it turns west while degenerating back to a wave
**For area of interest #26… consolidates into a single tropical low near 16N-34W by 66 hours and becomes a possible weak tropical cyclone near 17.5N-35W by 72 hours… the tropical cyclone becomes elongated southwest-northeast near 17.5N-40W by 108 hours with the elongated remnant low reaching 20.5N-40W by 168 hours
1800Z (Sep 9) NAVGEM Model Run...
**For Tropical Storm Francine…makes landfall over south-central Louisiana at 48 hours at hurricane strength… the gradually weakening inland remnant low then arcs north-northeast then north into the Ohio Valley region through 96 hours then dissipates over central Illinois after 120 hours
**For area of interest #23… through 60 hours drifts southwest while losing dominance to adjacent area of interest #26 to its east
**For area of interest #26… consolidates into a single tropical low near 18.2N-37W at 66 hours… tropical cyclone formation suggested near 20N-46W through 108 hours which proceeds to acquire hurricane strength while reaching 21.5N-56W through 168 hours
**Upper vorticity that passes over Francine’s inland circulation teams up with upper vorticity later deposited into the western Atlantic by what is currently the western Canada upper trough to generate a surface frontal low southeast of the Carolinas by 114 hours… frontal low evolves into possible subtropical cyclone located near 31.5N-71.2W through 168 hours
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