MY 2024 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #59

*******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 AUGUST 4 2024 3:26 PM EDT...

See Tropical Storm Debby section below for more information on its forecast and expected impacts across the southeastern United States from Florida to the Carolinas. See area of interest #16 section below for information on the central Atlantic tropical wave of low pressure currently approaching the southern Lesser Antilles which has become better organized under better than previously forecasted upper winds... interests across Jamaica and eastern Cuba should also be watching this wave as another round of favorable upper winds is possible over the wave by late this week.

Further east... satellite imagery over Africa suggests the African Easterly Jet and associated surface tropical waves of low pressure are positioned further north. This will likely make the waves prone to ingesting dry air from the north Africa Sahara desert as they later move southwestward into the eastern tropical Atlantic around the southeast side of the Atlantic surface ridge... in fact this has recently been seen by the tropical wave that has recently moved southwest to 13N-26W over this weekend. None of the current computer model runs are developing these waves.

TROPICAL STORM DEBBY... Debby continues to arc northward across the eastern Gulf of Mexico en route to northern Florida toward a deep-layer ridge weakness associated with an eastern North America surface frontal system and upper trough. Outflow and thunderstorms on the west side of the storm appear to have become undercut by westerly shear on the northwest side of the upper anticyclone that the storm was previously flourishing under and out ahead of the eastern North America upper trough. As such the majority of the thunderstorm activity has become lopsided toward the east half of the circulation. In the next 48 hours it appears the models are relying on Debby’s thunderstorm latent heat release to shape the upper wind profile. During this time a cool core east-west band of upper vorticity left behind by the eastern North America upper trough gets tossed toward the storm. In the next 24 hours the GFS which is bullish on Debby’s development has the storm’s northern outflow and thunderstorm latent heat release fight back the incoming upper vorticity band… reducing the shear and allowing the storm’s northern outflow to be enhanced by the flow streaming into the upper vorticity band. Because the west half of the thunderstorm field has already been eroded by shear I don’t think this scenario is as likely… and I agree with the NHC that Debby makes landfall no higher than an 85 mph maximum sustained wind hurricane in the far eastern panhandle or northwest Florida peninsula coast in 24 hours. I also think an eastward slant in the north track should be occurring by that time due to the upper westerlies of the upper vorticity band… thus my forecast landfall location is slightly east of the 0600Z GFS run which has a weaker and more north upper vorticity band for the reasons discussed above. Between 24 and 48 hours the models agree the upper vorticity band is shaped into an upper vortex trapped between upper ridging to the east bolstered by Debby’s thunderstorm latent heat release and western US upper ridge… with Debby show to be kicked east toward coastal Georgia by the southeast quadrant of the upper vortex. Dropping wind shear levels and the eastern divergence zone of the vortex should help slow Debby’s weakening rate over land… which is why I show a 50 mph max wind tropical storm by 48 hours despite a one-day stretch over land.

What happens to Debby beyond 48 hours is getting complicated as shown by the completely different long range solutions between the usually reliable GFS and ECMWF models. The ECMWF has Debby and the upper vortex kicked east the shortwave upper trough expected to roll through the Ohio Valley and NE US… then has Debby eventually escaping the grip of the upper vortex while transitioning into a less tropical system engaged with and supported by the next upper trough that slides across North America… resulting in a northeast long-range track across the inland areas of the Carolinas and then parallel to the northeast US shoreline. Meanwhile in the GFS the Debby and upper vortex pair have no interaction with the passing Ohio Valley shortwave upper trough… with the upper vortex and Debby retrograding southwest back toward the northern Gulf of Mexico while the upper vortex gets pushed around the western US upper ridge and Debby constantly getting tugged toward the core of the retrograding upper vortex. My updated forecast track splits the difference between the two ideas and has a quasi-stationary system at the Georgia/South Carolina border region from 72 to 120 hours until we know which of these two extremes becomes the most likely… it’s also not impossible for Debby to also end up being quasi-stationary too as the model split also indicates conflicting steering influences. The details in my quasi-stationary forecast track are based on Debby making a slow clockwise looping arc from 48 to 96 hours while steered by the east side of the upper vortex… with the west bend from 72 to 96 hours assuming for now Debby misses interaction with the passing Ohio Valley shortwave upper trough and slips west under the influence of surface ridging the flares up under the upper convergence behind the shortwave. Then between 96 and 120 hours I show a northeast drift due to the flow ahead of a possible approaching surface frontal low that develops with the support of the next upper trough that slides across North America. Note from the Florida landfall time through 120 hours my weakening rate remains slow due to proximity to offshore warm waters… the supporting eastern divergence zone of the upper vortex through 96 hours… then a supportive upper anticyclone with outflow by 120 hours as the upper vortex retrogrades southwest and away… with the anticyclone a manifestation of higher pressures between the retrograding SE US upper vortex and western Atlantic upper vortex which could also be retrograding toward Debby while its pushed around by the northwest Atlantic upper ridge (more on the west Atlantic upper vortex is in the area of interest #16 section below).

Regarding impact to land areas:

(1) The western half of the Florida peninsula will see gusty winds with isolated damage potential and coastal surf in addition to the heavy rains bands in the next 24 hours. Interests across the northern-third of the Florida peninsula… southeastern Georgia… and far eastern Panhandle should be adapting to the latest forecast by rushing preparations to completion by this late afternoon for the following: heavy rains with flash flood potential… potential for widespread damage from coastal storm surge and hurricane-force winds to arrive on the northwest Florida peninsula coast or far eastern Florida panhandle coast… with strong winds with damage potential spreading inland across the northern-third of the peninsula… far eastern panhandle… and southeastern Georgia through Monday. Coastal Georgia and northeastern Florida will see an increase in coastal surf as the center of Debby is bent east toward the Atlantic.

(2) After Monday… it has become likely Debby bends northeast then north into the Carolinas… with the forecast track weighted toward South Carolina at this time. As such I recommend South Carolina (both coastal and inland areas) to begin preparing for tropical storm force conditions (gusty winds with some damage potential… coastal surf… and heavy rains with flash flood potential).

Update as of 2 PM EDT... latest data gathered by the NHC shows that Debby has intensified further to 65 mph maximum sustained winds. Recent satellite frames show a flare up of thunderstorms just northeast of the surface center being wrapped into the center... which could be an indication in a drop in wind shear as the 0600Z GFS model run was predicting as discussed above. For 11 AM EDT the NHC has increased their intensity forecast to 90 mph maximum sustained winds for the north Florida landfall time... and I agree while also increasing my intensity forecast to this level for 1200Z August 5.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1200Z Aug 4)... 60 mph maximum sustained wind tropical storm centered in the eastern Gulf of Mexico at 26.3N-84.2W

IOH 24 Hr Forecast (1200Z Aug 5)... 90 mph maximum sustained wind hurricane making landfall in north Florida just south of Perry at 29.8N-83.5W

IOH 48 Hr Forecast (1200Z Aug 6)... 50 mph maximum sustained wind tropical storm centered over southeastern Georgia at 31.2N-82W

IOH 72 Hr Forecast (1200Z Aug 7)... 50 mph maximum sustained wind tropical storm centered over the southern tip of South Carolina at 32.5N-81W

IOH 96 Hr Forecast (1200Z Aug 8)… 40 mph maximum sustained wind tropical storm centered inland just west of the South Carolina/Georgia border at 32.5N-82W

IOH 120 Hr Forecast (1200Z Aug 9)… 35 mph maximum sustained wind tropical depression centered over southern South Carolina near 33N-81W

*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT************************

Landfall (1200Z Aug 5)... 90 mph maximum sustained wind hurricane making landfall just southwest of Perry Florida at 29.9N-84.1W

Landfall (1200Z Aug 8)... 45 mph maximum sustained wind tropical storm centered centered just inland of the northeastern South Carolina coast at 33.5N-79.5W

5-Day Position (1200Z Aug 9)... 35 mph maximum sustained wind tropical depression centered over eastern North Carolina at 35.5N-78W

AREA OF INTEREST #16... The central Atlantic tropical wave of low pressure that continues to approach the southern Lesser Antilles continues to show signs of organization with curved bands of showers and thunderstorms. Instead of suppressing upper vorticity increasing over the wave due to relatively lower pressures between the northwest Atlantic upper ridge and eastern tropical Atlantic upper ridge... the tropical wave has been thriving beneath the outflow of ongoing tropical upper ridging in relatively higher pressures south of the current western Atlantic upper vortex. The NHC has upgraded this tropical wave to a new area of interest for possible tropical cyclone formation... this marks the sixteenth tropical Atlantic area of interest tracked on this site this year.

Forecast track in the outlook below is based on the wave continuing west-northwest around the southwest quadrant of the steering Atlantic surface ridge and toward the ridge weakness associated with Debby. Noting the long-range forecast for Debby has greater than usual uncertainty... and future shifts in the forecast track of Debby will result in long-range track adjustments for this area of interest as well. Regarding the upper-wind profile... this area of interest will be contending with the current western Atlantic upper vortex which shifts south toward the eastern Caribbean under the influence of Debby's outflow in the early part of the forecast period. I already start off with elevated odds of tropical cyclone formation as high as 50% as this system crosses the Lesser Antilles and eastern Caribbean due to the high organization it is currently exhibiting and ongoing favorable short-term upper-level winds... and decrease odds to 20% by 72 hours as westerly shear encroaches from the southward-sagging western Atlantic upper vortex. Noting in the latter part of the 5-day forecast period the northwest Atlantic upper ridge re-builds after being initially disrputed by the passage of the current eastern North America upper trough... and the upper ridge is expected to push the upper vortex northwestward and away toward the United States east coast. As such a favorable upper anticyclone has potential to expand over this area of interest and in the wake of the retreating upper vortex which explains why I trim odds of tropical cyclone formation back upward by day 5.

Regardless of tropical cyclone formation or not... expect heavy rains and gusty winds across the southern Lesser Antilles in the next 24 hours. I recommend interests in Jamaica and eastern Cuba begin to monitor the progress of this tropical wave.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1200Z Aug 5)... 50% chance of tropical cyclone formation (just east of the southern Lesser Antilles near 12N-60W)

IOH 48 Hr Outlook (1200Z Aug 6)... 40% chance of tropical cyclone formation (eastern Caribbean Sea near 13N-65W)

IOH 72 Hr Outlook (1200Z Aug 7)... 20% chance of tropical cyclone formation (central Caribbean Sea near 15N-70W)

IOH 96 Hr Outlook (1200Z Aug 8)... 20% chance of tropical cyclone formation (southwest of Haiti near 16.5N-75W)

IOH 120 Hr Outlook (1200Z Aug 9)... 40% chance of tropical cyclone formation (between western Jamaica and eastern Cuba near 19N-78.5W)

*****National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT**************************

Formation chance through 48 hours... 10%

Formation chance through 7 days... 20%

...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).

0000Z (Aug 4) CMC Model Run...

**For Tropical Storm Debby… makes landfall over the eastern Florida panhandle as a high-end tropical storm just after 30 hours… subsequently pulled east across South Georgia by a cut-off upper vortex left behind by eastern North America upper trough and reaches coastal Georgia by 90 hours as a subtropical cyclone supported by the eastern divergence zone of the vortex… swings west back into southern Georgia by 126 hours while pulled in by upper vortex and begins to weaken as an inland remnant subtropical low while becoming exposed to suppressing convergence on NW side of the upper vortex… as upper vortex moves into Georgia the fading remnant surface low becomes quasi-stationary and trapped under the vortex through 168 hours

**For area of interest #16… tropical wave becomes a Caribbean tropical low near 14.8N-78.5W at 102 hours and strengthens into a compact tropical cyclone by 120 hours while located near 16.5N-81W… makes landfall on the northeast corner of the Yucatan peninsula as a compact hurricane just after 156 hours and emerges into the Gulf of Mexico from the northwestern part of the peninsula by 168 hours

0000Z (Aug 4) ECMWF Model Run...

**For Tropical Storm Debby… makes landfall over the far eastern Florida panhandle as a hurricane at 36 hours… subsequently pulled east across South Georgia by a cut-off upper vortex left behind by eastern North America upper trough and reaches coastal Georgia by 72 hours as a tropical cyclone aided by the eastern divergence zone of the vortex… as the upper vortex drifts east offshore the tropical cyclone continues east into offshore waters and then hooks north toward the Carolina coast through 90 hours while regaining hurricane strength… makes landfall at the NC/SC border by 102 hours and weakens to an inland tropical storm moving north-northeast across eastern North Carolina through 126 hours… subsequently the next upper trough approaching collapses into an east-west band along the US/Canada border under influence of west Canada hot air mass upper ridge with a shortwave upper trough on south side of the band scooping Debby across southwest Virginia and into offshore Atlantic waters as a remnant frontal cyclone supported by the shortwave… center of remnant frontal cyclone east-southeast of Cape Cod Massachusetts by 168 hours

**For area of interest #16… no development shown through 168 hours (development suggested in Bay of Campeche not long after 168 hours)

0600Z (Aug 4) GFS Model Run...

** For Tropical Storm Debby... makes landfall over the far eastern Florida panhandle as a hurricane at 30 hours… subsequently pulled east across South Georgia by a cut-off upper vortex left behind by eastern North America upper trough and reaches coastal Georgia by 69 hours as a tropical cyclone aided by the eastern divergence zone of the vortex... after briefly moving offshore the northeast quadrant of the upper vortex then pulls the tropical cyclone northwest for a landfall just southwest of the GA/SC border at 99 hours… as a gradually weakening inland remnant low continues west into east-central Alabama by 126 hours… subsequently the upper vortex retrogrades southwest into the Gulf of Mexico which pulls the fading remnant low southwest into the Alabama Gulf coast through 168 hours

**For area of interest #16... no development shown

0600Z (Aug 4) NAVGEM Model Run...

**Not available at above-mentioned source