*******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.*********
...THURSDAY SEPTEMBER 5 2024 11:59 PM EDT...
The Atlantic tropics remain very busy with now five 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. Note that I have continued shorthand outlooks on some areas of interest that do not have a specific track forecast for each 24-hour period… to ensure this update is released in a timely manner given the number of concurrent areas of interest in progress. Also note the following regarding impact to land areas:
(1) Area of interest #19 may bring impacts to the Yucatan peninsula by this weekend... and northeast Mexico after the weekend.
(2) Area of interest #23 may bring impacts to the Republic of Cabo Verde Islands within the next 72 hours
(3) Area of interest #24 will bring impacts to the northeast US coast and portions of Atlantic Canada thru 48 hours regardless of tropical characteristics or not.
In addition to the current areas of interest… watching for the possible emergence of two more in the days ahead as follows:
(1) The south part of the current North Atlantic upper trough is expected to become a cut-off upper vortex… within the next couple of days the eastern divergence zone of the vortex may trigger a frontal low with possible short-lived tropical characteristics well to the east-southeast of Newfoundland. Have not marked an area of interest for this situation at present as not all models agree on positioning the forecast frontal low over sufficiently warm water.
(2) A tropical wave of low pressure is defined on satellite over central Africa… some models already agree on developing this wave when it later moves into the eastern and central tropical Atlantic after day 4.
AREA OF INTEREST #19... The tropical wave of low pressure that was previously over the eastern Caribbean struggled to organized in the central Caribbean on Wednesday while passing through an axis of disrupting upper vorticity. However while now in a low shear and upper outflow environment in the western Caribbean... underneath the southeast side of the upper ridge centered in the western Gulf of Mexico... the tropical wave is attempting to organize while displaying a gyre of thunderstorms... albeit in the most recent satellite frames the gyre is less organized while thunderstorms are congregating away from the center of the gyre and to the south and east over Central America and adjacent Caribbean waters. Due to the recent disorganization trend... I currently forecast a 0% chance of tropical cyclone formation over the next 48 hours as the wave will run out of time to develop before crossing Belize and the Yucatan peninsula. While in the Bay of Campeche and western Gulf of Mexico... the tropical wave is expected to merge with area of interest #25 from the north by 72 hours and I still anticipate a 0% chance of tropical cyclone formation through that time as the merged system is likely to be broad in nature without a well-defined center. By 96+ hours... the merged system is then expected to curve northwest toward northeastern Mexico while pushed by the southwest side of the surface ridge currently behind the central North America surface front... as that surface ridge later descends into the eastern US. Despite remaining under the favorable upper winds associated with the western Gulf of Mexico upper ridge... I agree with the NHC's low 20% odds of tropical cyclone formation (for the 96 to 120 hour window) as I question if the merged system will have enough time to develop a well-defined center before landfall with northeastern Mexico. Note that regardless of tropical cyclone formation or not... the Yucatan peninsula of Mexico and Belize may see heavy rainfall and gusty winds from this system by this weekend.... followed by northeastern Mexico by early this upcoming week.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 20% (western Gulf of Mexico and northeastern coastal Mexico)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 20%
AREA OF INTEREST #21... The tropical wave of low pressure in the central tropical Atlantic is now positioned just east of the northern Lesser Antilles and has failed to develop so far while dry Saharan air prevented the wave from having organized thunderstorms. Over the next three days the tropical wave is forecast to angle west-northwest toward the waters just north of the northeastern Caribbean Islands... at first due to the surface ridge weakness associated with area of interest #24... followed by maintenance of the weakness as the current central North America surface front moves offshore. The warm surface southerly flow ahead of the surface front will help bolster a warm core northwest Atlantic upper ridge that will help push the neighboring upper vorticity string somewhat to the west. However the tropical wave will still walk into the upper vorticity by day 3... therefore time for this wave to develop has run out as it will now increasingly slip into a suppressed outflow regime beneath the upper vorticity. I plan this to be my final statement on this area of interest on this blog as I anticipate the wave to soon be removed from the NHC tropical weather outlook.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 3 days... 0% (north of the northeastern Caribbean Islands)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 0%
AREA OF INTEREST #23... The tropical wave of low pressure in the eastern tropical Atlantic has continued west to 12.5N-35W... and has also become less active and unorganized due to regional dry Saharan air. For the next 24 hours the tropical wave is likely to continue toward 40W longitude after which time the situation becomes more complex. For now the model consensus is the wave will spend 24 to approximately 72 hours meandering and potentially reversing eastward in track due to the surface ridge weakness forecast to develop in the eastern Atlantic as the south part of the current north Atlantic upper trough becomes a cut-off upper vortex whose divergent eastern side creates the weakness. During this same timeframe the large tropical wave of low pressure over western Africa moves offshore and also helps to pull the tropical wave associated with this area of interest potentially eastward. By 72 hours the two waves are likely to merge into a surface trough extending from the Republic of Cabo Verde Islands to 40W longitude. By 96 and 120 hours the cut-off upper vortex (due to prolonged isolation from high-latitude cold air) and associated surface ridge weakness decays... and the Atlantic surface ridge recovers due to the eastern convergence zone of an amplified upper ridge moving in from the northwest Atlantic (area of interest #21 section above discusses why the northwest Atlantic upper ridge materializes). The surface trough is likely to shift west with time as the recovered Atlantic surface ridge takes over the steering. For day 5 I agree with the NHC in showing low 10% odds of tropical cyclone formation as any surface trough that solidifies in the region will need time to establish a well-defined surface center... and its possible the surface trough fails to undergo tropical development while suffering from ongoing regional dry Saharan air.
For now the current eastern Atlantic tropical wave passed south of the Republic of Cabo Verde Islands without providing much rainfall to the islands. However by 72 hours the islands may see a round of heavy rainfall from the large tropical wave of low pressure currently over western Africa as that wave later moves offshore.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 5 days... 10% (central tropical Atlantic near 15N-40.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 10%
AREA OF INTEREST #24... A frontal low pressure area that was offshore of the Carolinas on Tuesday has proceeded to become a tropical area of interest in the Atlantic basin while at times developing strong thunderstorms just east of its center. As of 0000Z earlier this evening it was centered at 34.5N-70W... or midway between North Carolina and Bermuda. Recently the frontal low has been enhanced by the divergence zone of a low-amplitude upper trough that has accelerated into the northeastern US from the central US. Over the next 24 hours... as the upper trough moves from the northeastern US and into the northwest Atlantic... it is forecast to gain amplitude while becoming embedded within an amplifying warm core upper ridge (see area of interest #21 section above for why the northwest Atlantic upper ridge materializes). Increasing divergence on the east side of the amplifying upper trough is expected to strengthen the surface frontal low... and the 24-hour forecast point in the outlook is based on the position of the upper trough's divergence maximum. The amplification of the upper trough also means a reduction in wind shear... therefore the thunderstorms east of the center may be able to wrap around the center and resemble a subtropical cyclone that is simultaneously supported by the warm core outflow generated by the thunderstorm latent heat release. My odds of subtropical cyclone formation are set slightly higher than the NHC as of this writing... at 40%... due to the persistent strength of the thunderstorms that have been firing just east of the center over the last couple of days (although the thunderstorms dwindled around 1800Z earlier this evening... they have recovered in recent satellite frames). After 24 hours the northwest Atlantic upper ridge shifts off to the east... with the upper trough and surface frontal cyclone shifting north-northeast around the upper ridge and into Atlantic Canada. At this point this system will be over waters too cool for tropical characteristics... thus I end my outlook at 48 hours. Beyond 48 hours this system is expected to lose its identity over southeastern Quebec while becoming absorbed by the incoming upper trough/surface frontal system now approaching from central North America.
Regardless of tropical characteristics or not… this system is expected to bring a period of coastal surf… gusty winds… and possibly heavy rain to Nova Scotia… Prince Edward Island… and southeastern Quebec this weekend. Coastal surf may also develop along the northeastern US coast in the next 24 hours.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 7)... 40% chance of subtropical cyclone formation (northwestern Atlantic near 39.8N-66W)
IOH 48 Hr Outlook (0000Z Sep 8)... 0% chance of subtropical cyclone formation (central Gulf of St Lawrence near 46.5N-60.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 10%
AREA OF INTEREST #25... For the northwestern Gulf of Mexico and vicinity... the tail end of an old surface cold front has been enhanced into a new tropical low over the last couple of days due to a combination of divergence of the upper trough that recently ejected from the central US (now over the northeast US)… divergence ahead of the currently approaching central North America upper trough… and outflow on the north side of the sprawling upper ridge centered over the western Gulf of Mexico. Over the next couple of days the tropical low is expected to drift south due to the strength of the surface ridge that builds behind the central North America upper trough and fujiwhara interaction with area of interest #19 approaching from the southeast. It appears this system has already succumbed to westerly shear on the north side of the Gulf upper ridge while recently losing organized thunderstorms on the more recent satellite frames… and I currently assess area of interest #19 which has an advantage to develop further while located in a lower shear environment to the south is likely to become the dominant and absorbing feature in the fujiwhara interaction. Therefore I have assigned a 0% chance of tropical cyclone formation for this area of interest thru day 2… after which time absorption into area of interest #19 is expected to be completed. This is my planned final statement on this area of interest unless it continues to be mentioned in the NHC outlook by my next update.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 2 days... 0% (northwestern Gulf of Mexico)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 10%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
1200Z (Sep 5) CMC Model Run...
**For area of interest #19 currently in the western Caribbean… merges with area of interest #25 currently in the northwestern Gulf of Mexico through 72 hours… the tropical low that results from the merger makes landfall just south of the Texas/Mexico border at 120 hours then turns north and drifts into southern Texas through 168 hours
**For area of interest #21 currently east of the northern Lesser Antilles… no development shown
**For area of interest #23 currently in the eastern tropical Atlantic… through 72 hours retrogrades east due to tug of neighboring tropical wave to the east and becomes a possible compact tropical cyclone during that time… subsequently reverses to a west-northwest course to 17N-51.5W through 168 hours while staying a weak tropical low/cyclone
**For area of interest #24 currently midway between North Carolina and Bermuda… strengthens into a surface cyclone with possible tropical characteristics while reaching 39.5N-68W through 36 hours… as a cyclone losing tropical characteristics makes landfall over western Nova Scotia by 54 hours… while over southeast Quebec loses identity to approaching frontal system to the west by 72 hours
**A north Atlantic cut-off frontal low similar to area of interest #24 develops near 39.8N-41W at 36 hours and possibly gains tropical character near 40N-45W at 48 hours… subsequently accelerates west-southwest while weakening to a dissipating surface trough through 72+ hours
**Tropical wave emerges from west coast of Africa at 96 hours and accelerates west toward area of interest #23 through 168 hours while possibly becoming a weak tropical low or cyclone
1200Z (Sep 5) ECMWF Model Run...
**For area of interest #19 currently in the western Caribbean… merges with area of interest #25 currently in the northwestern Gulf of Mexico through 114 hours which results in a north-south surface trough… surface trough turns northwest into Texas and Oklahoma through 168 hours
**For area of interest #21 currently east of the northern Lesser Antilles… no development shown
**For area of interest #23 currently in the eastern tropical Atlantic… through 102 hours retrogrades northeast due to tug of neighboring tropical wave to the east and becomes a tropical low during that time… subsequently turns west-northwest through 168 hours with no further development shown
**For area of interest #24 currently midway between North Carolina and Bermuda… strengthens into a surface cyclone with possible tropical characteristics while reaching 39.5N-67.5W through 36 hours… as a cyclone losing tropical characteristics makes landfall over central Nova Scotia by 60 hours… while over southeast Quebec loses identity to approaching frontal system to the west by 78 hours
**A north Atlantic cut-off frontal low similar to area of interest #24 develops near 42.5N-40.5W at 30 hours… subsequently accelerates west-southwest while weakening to a dissipating surface trough through 60+ hours (frontal low stays north of 26 deg C sea surface temperature isotherm during lifecycle such that it doesn’t gain tropical character in this model run)
**Tropical wave emerges from west coast of Africa at 108 hours and passes over the Republic of Cabo Verde Islands through 132 hours while becoming a tropical cyclone… tropical cyclone then accelerates west toward area of interest #23 through 168 hours
1800Z (Sep 5) GFS Model Run...
**For area of interest #19 currently in the western Caribbean… merges with area of interest #25 currently in the northwestern Gulf of Mexico through 66 hours which results in a NW/SE tilted western Gulf surface trough… surface trough not shown to develop afterwards
**For area of interest #21 currently east of the northern Lesser Antilles… no development shown
**For area of interest #23 currently in the eastern tropical Atlantic… through 81 hours merges with tropical wave to the east resulting in a WSW/ENE tilted surface trough from 14N-40W to 16N-31.5W… slowly consolidates into a possible weak tropical cyclone near 16.5N-41.5W by 129 hours… weakens back to a tropical low while reaching 19N-52.5W by 165 hours
**For area of interest #24 currently midway between North Carolina and Bermuda… strengthens into a surface cyclone with possible tropical characteristics while reaching 40N-66W through 33 hours… as a cyclone losing tropical characteristics makes landfall over central Nova Scotia by 51 hours… while over southeast Quebec loses identity to approaching frontal system to the west by 72 hours
**Tropical wave emerges from west coast of Africa at 96 hours and passes just south of the Republic of Cabo Verde Islands as a disorganized tropical low through 129 hours… tropical low reaches 14N-36.5W by 165 hours
1800Z (Sep 5) NAVGEM Model Run...
**For area of interest #19 currently in the western Caribbean… merges with area of interest #25 currently in the northwestern Gulf of Mexico through 66 hours which results in a north-south elongated western Gulf surface trough… surface trough drifts southwest into the southwest Gulf through 102 hours due to strength of eastern US surface ridge… after surface ridge shifts east the surface trough turns north into Texas coast through 162 hours
**For area of interest #21 currently east of the northern Lesser Antilles… no development shown
**For area of interest #23 currently in the eastern tropical Atlantic… reaches 13N-41.5W at 84 hours while becoming a tropical low… becomes quasi-stationary here through 120 hours due to tug of tropical wave to the east… tropical low then turns west to 14.5N-49W through 168 hours
**For area of interest #24 currently midway between North Carolina and Bermuda… strengthens into a surface cyclone with possible tropical characteristics while reaching 40.2N-66.2W through 30 hours… as a cyclone losing tropical characteristics makes landfall over central Nova Scotia by 54 hours… while over southeast Quebec loses identity to approaching frontal system to the west by 72 hours
**A north Atlantic cut-off frontal low similar to area of interest #24 develops near 40.5N-41W at 30 hours… subsequently accelerates west-southwest and possibly gains tropical character near 39N-46.5W at 48 hours… subsequently turns west then north into waters southeast of Newfoundland where it loses identity to same frontal system that absorbs area of interest #24
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