*******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...SATURDAY SEPTEMBER 14 2024 10:52 PM EDT...
The surface and upper air charts valid for September 13 are added to this post... they were not initially generated and included to ensure a more timely release of the update.
...FRIDAY SEPTEMBER 13 2024 3:40 PM EDT...
The Atlantic tropics remain rather busy with the remnants of Francine centered over northeastern Arkansas... two areas of interest which have recently merged over the northern Lesser Antilles... Tropical Storm Gordon 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.
Elsewhere... watching for the possible emergence of additional areas of interest in the days ahead as follows:
(1) For the eastern tropical Atlantic... a tropical wave of low pressure has recently departed the west coast of Africa... however it is not upgraded to an area of interest at this time while ingesting dry Saharan air that has weakened its thunderstorm activity. Further east a pair of closely-spaced tropical waves of low pressure are over inland central and western Africa (see Africa satellite imagery at https://www.goes.noaa.gov/FULLDISK/GMIR.JPG). Steering current are expected to weaken in the eastern tropical Atlantic... due to the sprawling surface ridge weakness that will be associated with tropical cyclone Gordon and a central Atlantic surface front... and due to another surface ridge weakness toward northwestern Africa/southwestern Europe to be driven by the eastern divergence zone of the current eastward-shifting mid-latitude eastern Atlantic upper vorticity. It is possible the multiple tropical waves of low pressure merge in the eastern tropical Atlantic while running into each other as they move into the area of weak steering... which would result in a broad surface trough. And with the regional tropical upper ridge axis forecast to persist... featuring low shear and outflow... it is not out of the question that within the next week a meandering tropical disturbance emerges within the possible eastern tropical Atlantic surface trough.
(2) For the mid-latitudes of the central Atlantic... including the waters toward the west between Bermuda and the northeastern Caribbean Islands... area of interest #28 is forecast to develop near the United States east coast along the tail end of the regional surface front... and a northward-moving central Atlantic frontal cyclone is also expected to develop as covered in the Tropical Storm Gordon section below. The remainder of the surface front... in between the frontal cyclone and area of interest #28... may decay into one or more low pressure spins. For now I forecast tropical cyclone Gordon to dominate the surface inflow and upper outflow in the region through day 5... as such I currently do not forecast any of the potential mid-latitude central Atlantic spins to undergo tropical development. However should Gordon in fact dissipate into a remnant low as some of the models suggest... this may allow for one of the potential mid-latitude central Atlantic spins to become a new tropical area of interest in future updates... especially if one of the spins ends up in an area of lower shear to the south or west of the currently forecast central Atlantic complex upper trough (the details of the complex upper trough are in the Tropical Storm Gordon section below).
REMNANTS OF FRANCINE... While steered by upper vorticity that moved into the south-central US from the southwestern US... tropical cyclone Francine's center arced northward across western Mississippi then into northeastern Arkansas... and is becoming quasi-stationary in this region while whirling into the core of the upper vorticity. Ongoing weakening and then dissipation of Francine's remnant low is anticipated through this weekend due to a lack of supporting divergence beneath the core of the upper vorticity. The remaining effect of the fading remnant low is locally heavy rainfall over northeastern Arkansas and surrounding states... particularly further east across the southeastern United States where the region of supporting upper divergence (on the east side of the regional upper vorticity) has transferred. Gusty winds are no longer a concern with the fading remnant low. The following are the strongest wind gusts (in mph) that were generated by Francine at each of the following National Weather Service stations (weather.gov). Noting the winds tended to underperform further west in a corridor from Hammond Louisiana northward... across far western Mississippi... and eastern Arkansas (with the exception of Jonesboro) and over-performed toward the east while gusts toward 40+ mph clipped areas as far east as western Alabama and south-central Tennessee. This is a combination of Francine weakening a little faster than my previous intensity forecast and westerly wind shear associated with the aforementioned upper vorticity keeping the strongest weather lopsided to the east side of Francine's center. This will be my final statement on Francine on this blog as it is no longer a tropical cyclone.
**Abbeville (south-central LA)... sustained 30... gust 52... 6:53 PM CDT Sept 11
**Crowley (inland south-central LA)... sustained 26... gust 51... 5:53 PM CDT Sept 11
**Lake Charles (southwestern LA)... sustained 23... gust 31... 4:53 PM CDT Sept 11
**Morgan City (south-central LA)... sustained 44... gust 54... 4:56 PM CDT Sept 11 (weather station has had an outage since this report)
**Houma (southeastern LA)... sustained 52... gust 70... 6:55 PM CDT Sept 11
**New Orleans (southeastern LA)... sustained 39... gust 56... 8:53 PM CDT Sept 11
**Baton Rouge (inland southeastern LA)... sustained 23... gust 47... 10:53 PM CDT Sept 11
**Hammond (inland southeastern LA)... sustained 20... gust 35... 7:55 PM CDT Sept 11
**Gulfport (coastal MS)... sustained 33... gust 46... 12:53 AM CDT Sept 12
**Mobile (coastal AL)... sustained 26... gust 40... 11:53 PM CDT Sept 11
**Hattiesburg (inland southeastern MS)... sustanied 24... gust 40... 4:53 AM CDT Sept 12
**Monroeville (inland southwestern AL)... sustained 18... gust 35... 8:53 AM CDT Sept 12
**McComb (inland southwestern MS)... sustained 15... gust 31... 12:53 AM CDT Sept 12
**Jackson (inland southwestern MS)... sustained 21... gust 44... 10:53 AM CDT Sept 12
**Meridian (inland east-central MS)... sustained 21... gust 45... 9:58 AM CDT Sept 12
**Demopolis (inland west-central AL)... sustained 21... gust 30... 9:15 AM CDT Sept 12
**Tuscaloosa (inland west-central AL)... sustained 18... gust 39... 10:53 AM CDT Sept 12
**Tupelo (northeastern MS)... sustained 23... gust 37... 11:53 AM CDT Sept 12
**Vicksburg (MS near northern MS/LA border)... sustained 20... gust 31... 8:15 AM CDT Sept 12
**Tunica (northwestern MS)... sustained 22... gust 33... 1:55 PM CDT... 1:55 PM CDT Sept 12
**Brinkley (east-central AR)... sustained 23... gust 30... 3:56 PM CDT Sept 12
**Monticello (southeastern AR)... sustained 14... gust 23... 2:53 PM CDT Sept 12
**Jonesboro (northeastern AR)... sustained 21... gust 43... 6:53 PM CDT Sept 12
**Memphis (southwestern corner of TN)... sustained 28... gust 51... 4:54 PM CDT Sept 12
**Dyersburg (western TN)... sustained 25... gust 32... 6:56 PM CDT Sept 12
**Lawrenceburg (south-central TN near northwestern AL)... sustained 23... gust 39... 8:35 PM CDT Sept 12
**Nashville (north-central TN)... sustained 17... gust 32... 3:53 AM CDT Sept 13
**Sikeston (southeastern MO)... sustained 17... gust 26... 11:53 PM CDT Sept 12
**Poplar Bluff (southeastern MO)... sustained 16... gust 28... 7:53 PM CDT Sept 12
**Cape Girardeau (southeastern MO near MO/IL border)... sustained 15... gust 26... 9:53 PM CDT Sept 12
**Mayfield (southwestern corner KY)... sustained 9... gust 23... 12:53 PM CDT Sept 12
TROPICAL DEPRESSION SEVEN (RECENTLY UPGRADED TO TROPICAL STORM GORDON)... For much of the last 36 hours tropical depression seven in the eastern tropical Atlantic struggled to develop further as thunderstorms became lopsided to the east of the center from westerly shear associated with mid-latitude eastern Atlantic upper vorticity... and regional dry Saharan air may have also played a part in hampering development before this system moved into the shear. However as of 11 AM EDT today the depression developed a stronger thunderstorm cluster just east of center while also becoming a little better organized... enough for the NHC to finally upgrade it to Tropical Storm Gordon. Gordon is a little northeast of the previous forecast track line and so my updated one is adjusted accordingly... and calls for a slow down in forward speed and a gradual north turn through day 5 in weak steering currents that will be associated with an expansive surface ridge weakness to be associated with the surface front currently moving into the open central Atlantic... with the front being enhanced by a complex upper trough that will also be in the central Atlantic. The complex upper trough initially materializes from the merger of the upper trough that recently entered the northwest Atlantic from eastern Canada... and the upper trough currently over north-central Canada... the eastern divergence zone of which develops a strong frontal cyclone along the surface front that quickly pulls northward away from Gordon such that the ridge weakness is enough to slow Gordon's current west-northwest track while at the same time not close enough to heavily influence Gordon's track. The southwestern tail end of the complex upper trough is then maintained by some energy that ejects from the current western US upper trough that eventually works its way into the central Atlantic... with the divergence zone of the upper trough's southwestern tail helping to enhance what remains of the central Atlantic surface front such that I forecast Gordon to turn north by day 5 toward the front. My updated intensity forecast is notably lowered compared to the previous due the above-mentioned initial struggles that Gordon faced during its initial tropical depression phase... and as many of the recent global model runs actually want to dissipate Gordon as it will soon face northerly and then northeasterly shear while continuing on into the remainder western portion of the regional tropical upper ridge axis. My current intensity forecast keeps Gordon alive through the short-term 48-hour window of shear... then strengthens Gordon as it reaches the core of the tropical upper ridge axis where shear is lower and upper outflow is higher. However I do not strengthen Gordon into a hurricane as the recent ECMWF model runs do... out of conservativeness in case the other global models are right that Gordon in fact dissipates in the short-term. Noting that just after day 5 Gordon may face another round of wind shear that subsequently kneecaps its long-term intensity... as the southwestern tail of the complex upper trough digs southeast toward Gordon in the current long range computer model runs.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 13)... 40 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 19.4N-38.6W
IOH 24 Hr Forecast (1200Z Sep 14)... 40 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 20N-42W
IOH 48 Hr Forecast (1200Z Sep 15)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 20.5N-45W
IOH 72 Hr Forecast (1200Z Sep 16)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 21N-48W
IOH 96 Hr Forecast (1200Z Sep 17)... 60 mph maximum sustained wind tropical storm centered in the central Atlantic at 22.5N-49W
IOH 120 Hr Forecast (1200Z Sep 18)... 70 mph maximum sustained wind tropical storm centered in the central Atlantic at 25N-49W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT*************************
5-Day Position (1800Z Sep 16)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 20.4N-50.8W
AREA OF INTEREST #23... The pair of closely-spaced central Atlantic tropical low pressure swirls has continued west-northwest toward and then into the northern Lesser Antilles since my previous update... this area of interest was for tracking the eastern of the two spins in the pair. I suppose it was always going to be a tossup as to which of the two spins was going to dominate... and it appears the western of the two... tagged as area of interest #27 in this blog... has done so while beginning to absorb this area of interest. As such this area of interest has been cancelled in the NHC tropical weather outlook... and this will be my final statement on this area of interest (also for this final update... not providing an outlook with a track forecast as absorption into area of interest #27 will be completed soon).
AREA OF INTEREST #27... As noted in the above area of interest #23 section... the pair of closely-spaced central Atlantic tropical low pressure swirls has continued west-northwest toward and then into the northern Lesser Antilles since my previous update... this area of interest is for tracking the western of the two spins in the pair. Noting the tropical low is expected to continue west-northwest into the waters just north of Puerto Rico... while tracking toward the surface ridge weakness associated with area of interest #28. This feature did produce showers and thunderstorms over the northern Lesser Antilles this morning... which have since dwindled. The NHC 2 PM EDT tropical weather outlook cites dry air is the reason for this... and upper air analysis does show that toward the northwest upper convergence that would support dry sinking air is in progress on the east side of the upper ridge that has been centered over the western Gulf of Mexico over the last several days... and on the northwest side of a slowly-decaying band of upper vorticity that has been covering the eastern Caribbean and western Atlantic. Although upper winds may become more favorable for development after 24 hours... when the band of upper vorticity dissipates (which would allow the east side of the aforementioned upper ridge to cover this system with upper outflow)... the current assumption is area of interest #28 will begin to dominate the region which would cause this system to simply be absorbed by area of interest #28. Therefore assigning a 0% chance of tropical cyclone formation... and making this my planned final statement on this area of interest as the NHC also lowered development odds to 0% and will probably have this area of interest removed soon in its tropical weather outlook product.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 14)... 0% chance of tropical cyclone formation (just north of Puerto Rico near 19.5N-66.2W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 0%
AREA OF INTEREST #28... To the east of ex-Francine... a broad area of upper divergence associated with the east side of a lobe of upper vorticity is producing pockets of showers and thunderstorms across the southeastern United States... and over offshore waters the general upper divergence pattern is maintaining the tail end of a surface front as well as a new surface low just offshore of east-central Florida. Watching to see if this field of low surface pressures eventually consolidates into an offshore possible subtropical or tropical cyclone in the days ahead... especially if the upper vorticity remains amplified enough to keep wind shear lower and upper divergence elevated and concentrated enough to develop a well-defined surface spin. Global models... except the GFS... have trended away from subtropical or tropical cyclone development while the upper vorticity is not as amplified as previously forecast. In response I have lowered my peak odds of subtropical or tropical cyclone formation to 35% in this update cycle. Through 72 hours the upper divergence maximum of the upper vorticity sets up near 30N-75W... and this is the general area I expect a well-defined surface spin is most likely to develop. The steering from 72 to 120 hours hinges upon the final configuration the upper vorticity takes and also a blocking surface ridge to the north that takes shape under the western convergence zone of passing north-central Canada upper trough... followed by the convergence zone of energy that ejects from the current western US upper trough and heads toward tropical cyclone Gordon. Previously the models showed the upper vorticity acquiring an east-west oblong shape while merging with a second piece of energy that ejects from the current western US upper trough... now the models show the upper vorticity acquiring a more north-south oblong shape with the second piece of energy being positioned further north. This allows the steering flow to be more southerly and less easterly due to the shape of the upper vorticity... but also due to the eastern divergence zone of the north-south upper vorticity axis now being able to keep the overall strength of the blocking surface ridge lower. Therefore the long range track is less likely to be northwest into the Carolina coast... and more likely to instead angle north-northwest into the North Carolina Outer Banks and coastal mid-Atlantic region of the US. As such I recommend interests for the mid-Atlantic United States (from the North Carolina coast to coastal Maryland/Delaware) monitor the progress of this area of interest in the days ahead for possible subtropical or tropical cyclone impacts (such as gusty winds... heavy rainfall... and coastal surf) which would occur by the early part of this upcoming week.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
Formation chance through 4 days... 35% (just south of the North Carolina Outer Banks near 34.5N-75.8W)
Formation chance days 4 to 5... 0% (North Carolina/Virginia border near 36.5N-76W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 40%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 13) CMC Model Run...
**For tropical depression seven... degenerates into a broad surface trough near 19N-50W through 90 hours with no re-development shown thereafter
**For area of interest #23 currently in the central tropical Atlantic... no development shown
**For area of interest #27 currently moving into the northern Lesser Antilles... no development shown **For area of interest #28 (surface front currently offshore of the southeastern US)... no development shown
0000Z (Sep 13) ECMWF Model Run...
**For tropical depression seven... moves west-northwest to 21N-50W through 126 hours... subsequently turns north while strengthening into a tropical storm then hurricane while reaching 25.5N-51W through 168 hours
**For area of interest #23 currently in the central tropical Atlantic... no development shown
**For area of interest #27 currently moving into the northern Lesser Antilles... no development shown
**For area of interest #28 (surface front currently offshore of the southeastern US)... tail end of front gradually develops into a northward-moving surface low that reaches the waters just offshore of the North Carolina Outer Banks through 132 hours... surface low then becomes quasi-stationary at this location through 168 hours
0600Z (Sep 13) GFS Model Run...
**For tropical depression seven... degenerates into a broad surface trough near 18.8N-50W through 96 hours with no re-development shown thereafter
**For area of interest #23 currently in the central tropical Atlantic... no development shown
**For area of interest #27 currently moving into the northern Lesser Antilles... no development shown
**For area of interest #28 (surface front currently offshore of the southeastern US)... tail end of front develops into a surface low near 30N-75.5W through 51 hours... subsequently strengthens into a possible subtropical or tropical cyclone that arcs north-northwest resulting in a landfall at Cape Lookout North Carolina at 102 hours... weakening inland remnant low then transitions into a non-tropical frontal low that moves north-northwest into western Maryland through 135 hours... while then arcing west into the suppressive upper convergence zone of the overhead upper vorticity the inland remnant low dissipates over the Ohio/West Virginia border at 150+ hours.
**A portion of the surface front tied to area of interest #28 also develops into a small frontal depression southeast of Bermuda at 45 hours... frontal low increasingly strengthens while moving east-southeast to 29.5N-56W... frontal low reverses to a west-southwest drift to 28N-49W through 168 hours (tropical development of frontal low unlikely due to forecast westerly shear imparted by southwest side of current upper troughs over north-central and eastern Canada when the troughs merge in the Atlantic... followed by upper convergence on southeast side of deep-layer ridge by 168 hours that develops in the wake of the merged upper trough)
**A portion of the surface front tied to area of interest #28 also develops into yet another frontal low southeast of Bermuda by 69 hours... under steering influence of adjacent frontal low to the east it drifts south-southwest to 24N-63W through 168 hours (this feature has a better chance at transition to tropical character while eventually becoming embedded beneath core of deep-layer ridge where shear is low and upper outflow is possible).
**Tropical wave emerges from west coast of Africa at 72 hours with tropical cyclone formation suggested just east of the Republic of Cabo Verde Islands at 120 hours... while gradually drifting north into the waters offshore of Mauritania the tropical cyclone gradually strengthens through 168 hours
0600Z (Sep 13) NAVGEM Model Run...
**Not available at above-mentioned source
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