*******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 18 2024 9:35 PM EDT...
The surface and upper air charts valid for September 17 are added to this post... they were not initially generated and included to ensure a more timely release of the update.
...UPDATE...TUESDAY SEPTEMBER 17 2024 11:30 AM EDT...
As of 11 AM EDT... recent satellite data suggested Gordon no longer had a closed surface spin and the NHC abruptly downgraded Gordon to a remnant surface trough of low pressure. Due to the potential for the remnants of Gordon to re-generate into a tropical cyclone while turning north... the NHC will be carrying future statements on the remnants of Gordon as an area of interest in their tropical weather outlook... and likewise the remnants of Gordon will also be considered an area of interest in my next update.
...TUESDAY SEPTEMBER 17 2024 10:55 AM EDT...
Regarding current Atlantic tropical systems... Tropical Depression Gordon continues to move slowly in the open central Atlantic… see Gordon section below for more info. See area of interest #28 section below for an update on the disturbance that has recently moved into the Carolinas.
Elsewhere in the Atlantic basin… noting the following:
(1) For the eastern tropical Atlantic... a tropical wave of low pressure that recently emerged from western Africa is merging with another wave that has been offshore… and there is a high chance the multiple waves could merge into a surface trough. Steering currents 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 adjacent frontal low that will be interacting with Gordon… 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. Therefore the potential surface trough is expected to be slow-moving at a position southeast of tropical cyclone Gordon. 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 few days a meandering tropical disturbance emerges within the possible eastern tropical Atlantic surface trough.
(2) For the mid-latitudes of the central Atlantic... a frontal low is currently positioned near 30N-50W… however tropical development of this feature is not expected as Gordon is expected to toss this feature southwest into unfavorable upper winds… see Gordon section below for more information.
(3) The eastern divergence zone of the large-scale upper vorticity over the eastern US may produce another subtropical or tropical disturbance over waters offshore of the eastern US in the days ahead. In addition the south part of the upper vorticity may dive far south enough to enhance weather associated with the current central Caribbean tropical wave of low pressure… potentially resulting in a western Caribbean tropical disturbance in the days ahead.
TROPICAL DEPRESSION GORDON... While firing increasing thunderstorms across the southeast half of its circulation... Gordon continues to hang on as a tropical depression in the open central tropical Atlantic. In the upper-levels upper ridging has shifted eastward into the mid-latitudes of the central Atlantic from the western Atlantic while a tropical upper ridge axis persists to the south. A portion of southwestward-retrograding upper vorticity from the eastern Atlantic has become wedged in between the tropical-latitude and mid-latitude upper ridges. As of this writing the center of Gordon is below the upper vorticity... and the thriving thunderstorms southeast of the center are probably taking advantage of the outflow supplied by the tropical upper ridge. Going forward the models are converging on the following complex solution regarding Gordon's future... and my updated forecast below is adjusted accordingly:
(1) Over the next 48 hours... Gordon is expected to turn north then northeast while undergoing a fujiwhara interaction with the frontal low currently at 30N-50W. I do not forecast intensification through 24 hours as disruptive upper vorticity remains in Gordon's environment... however I begin to show intensification by 48 hours as Gordon moves into the low shear/upper outflow environment beneath the mid-latitude upper ridge... and many of the models are now showing Gordon surviving the short-term and re-intensifying while it curves northeast.
(2) Between 48 and 72 hours upper-level energy separating from the current eastern US upper vorticity field approaches Gordon and the adjacent frontal low undergoing a fujiwhara interaction with Gordon. The fujiwhara interaction tosses the frontal low southwest directly below the upper-level energy where upper divergence is lacking which should cause the adjacent frontal low to not undergo tropical development and instead weaken... and by 72 hours divergence on the east side of the upper-level energy may help Gordon intensify further. By 96 hours I forecast weakening as southwesterly shear increases when the upper-level energy nears.
(3) In the 72 to 120 hour window... a series of surface frontal lows enter the north Atlantic from Canada while supported by the current central Canada upper trough when it enters the north Atlantic... followed by an additional upper trough that follows behind... also noting the two upper troughs may merge into an oblong upper vortex. The warm sector of the series of north Atlantic frontal lows is forecast to support warm core deep-layer ridging north of Gordon and the upper-level energy incoming to Gordon's west... with the amplifying deep-layer ridge causing the upper-level energy to also amplify into a possible cut-off upper vortex. I hook Gordon's track straight north along the east side of the potential upper vortex in the 96 to 120 hour window... and I forecast some slight re-strengthening during that time due to possible divergence on the east side of the vortex. If the current forecast holds... the close proximity of Gordon to the upper vortex may cause it to more resemble a subtropical instead of a fully tropical system by 120 hours.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Sep 16)... 35 mph maximum sustained wind tropical depression centered in the central tropical Atlantic at 19N-48.5W
IOH 24 Hr Forecast (1800Z Sep 17)... 35 mph maximum sustained wind tropical depression centered in the central Atlantic at 21N-50W
IOH 48 Hr Forecast (1800Z Sep 18)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 23N-48W
IOH 72 Hr Forecast (1800Z Sep 19)... 60 mph maximum sustained wind tropical storm centered in the central Atlantic at 26N-45W
IOH 96 Hr Forecast (1800Z Sep 20)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 28.5N-41.5W
IOH 120 Hr Forecast (1800Z Sep 21)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 32N-41.5W
*****National Hurricane Center (hurricanes.gov) official forecast as of 11 PM EDT*************************
5-Day Position (0000Z Sep 22)… 60 mph maximum sustained wind tropical storm centered in the central Atlantic at 29.5N-43.5W
AREA OF INTEREST #28 (POTENTIAL TROPICAL CYCLONE EIGHT)… Satellite image of frontal low with tropical characteristics making landfall at the North Carolina/South Carolina border around 1800Z on Monday September 16:
As expected… the frontal low with strong thunderstorm activity that was offshore of the Carolinas over the weekend pivoted west into the Carolinas on Monday while guided by the steering flow between the surface ridge to the north and inland upper vorticity to the west. Gusty winds… heavy rainfall… and coastal surf impacted northeastern South Carolina and southeastern North Carolina… and by Monday evening gusty winds spread across much of the inland regions of North Carolina due to the pressure gradient between the north side of the frontal low and surface ridge. Any wind gusts that are still occurring across North Carolina should diminish today as the frontal low weakens while moving beneath the part of the upper vorticity that lacks divergence. Based on the latest radar… the rainfall has become more scattered and overspreads central and southern Virginia… southern West Virginia… and eastern Kentucky where locally heavy downpours with flash flooding cannot be ruled out. The latest model guidance suggests this diminishing system may not swing west past the Appalachian mountains while potentially tugged back east by offshore western Atlantic pressure falls to be induced by the divergence zone of the regional upper vorticity… will watch to see if another subtropical or tropical disturbance develops in the waters offshore of the eastern US in the days ahead. Meanwhile this is the final statement on this area of interest on this blog as tropical development is no longer possible due to the landfall… and likewise the NHC removed this area of interest from their products overnight.
The following are the strongest wind gusts (in mph) that were generated by this disturbance at each of the following National Weather Service stations (weather.gov).
**Myrtle Beach (northeastern coastal SC)... sustained 26... gust 37... 10:56 AM EDT Sept 16
**Georgetown (northeastern coastal SC)... sustained 17... gust 29... 1:55 PM EDT Sept 16
**Florence (northeastern inland SC)... sustained 26... gust 44... 2:53 PM EDT Sept 16
**Sumter (inland central SC)... sustained 31... gust 30... 4:55 PM EDT Sept 16
**Wilmington (coastal southeastern NC)... sustained 29... gust 45... 10:53 AM EDT Sept 16
**Lubmerton (inland southeastern NC)... sustained 23... gust 43... 12:56 PM EDT Sept 16
**Morehead City (coastal southeastern NC)... sustained 14... gust 37... 1:58 PM EDT Sept 16
**Fayetteville (inland southeastern NC)... sustained 24... gust 40... 4:53 PM EDT Sept 16
**Raleigh (central NC)... sustained 17... gust 32... 11:51 PM EDT Sept 16
**Asheboro (west-central NC)... sustained 17... gust 31... 8:25 PM EDT Sept 16
**Greensboro (northwestern NC)... sustained 21... gust 39… 3:54 AM EDT Sept 17
**Charlotte (southwestern NC)... sustained 22... gust 39... 8:52 PM EDT Sept 16
**Elizabeth City (northeastern NC)... sustained 23... gust 32... 12:54 PM EDT Sept 16
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 16) CMC Model Run...
**For Tropical Depression Gordon... weakens to a remnant low near 19N-48.5W at 24 hours... subsequently the remnant low turns on a northeast drift while pulled by adjacent frontal low to the northwest and regains tropical cyclone status near 24N-46.2W at 102 hours and gains hurricane strength while reaching 26N-45.5W through 156 hours... hurricane reaches 27.5N-46.2W by 168 hours
**For area of interest #28... makes landfall on the northeastern South Carolina coast at 24 hours while potentially becoming a subtropical or tropical cyclone... the weakening inland remnant low continues northwest to the NC/TN border through 66 hours where it proceeds to dissipate
**For current central Caribbean tropical wave (formerly tagged area of interest #23 on this blog)... moves slowly west and evolves into a broad tropical low near 13N-80W at 108 hours... while moving north-northwest the broad tropical low strengthens to a tropical depression centered offshore of the Nicaragua/Honduras border at 144 hours... strengthens further to a broad tropical storm centered northeast of eastern Honduras through 156 hours... center of the gradually strengthening tropical storm accelerates north and passes just west of the Cayman Islands by 168 hours
0000Z (Sep 16) ECMWF Model Run...
**For Tropical Depression Gordon... weakens to a remnant low near 19.5N-50W through 36 hours... subsequently the remnant low turns on a northeast drift while pulled by adjacent frontal low to the northwest and regains tropical cyclone status near 26N-47.5W at 108 hours... gains hurricane strength while continuing north to 30N-47.5W through 156 hours... hurricane turns northeast to 31.5N-46.5W through 168 hours
**For area of interest #28... makes landfall on the northeastern South Carolina coast at 18 hours while potentially becoming a subtropical or tropical cyclone... the weakening inland remnant low continues west to the Georgia/South Carolina border through 54 hours where it proceeds to dissipate
0600Z (Sep 16) GFS Model Run...
**For Tropical Depression Gordon... weakens to a remnant low near 19N-49W at 24 hours... subsequently turns north then northeast while pulled by adjacent frontal low to the northwest and regains tropical cyclone status near 31.5N-39.5W at 120 hours... while remaining a weak tropical cyclone it turns west-northwest then northeast and reaches 36.5N-39W by 168 hours
**For area of interest #28... makes landfall on the northeastern South Carolina coast at 9 hours while potentially becoming a subtropical or tropical cyclone... the weakening inland remnant low continues west to the Georgia/South Carolina border through 36 hours where it proceeds to dissipate
0600Z (Sep 16) NAVGEM Model Run...
**Not available at above-mentioned source
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