*******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 11:20 AM EDT...
Satellite image of strengthening Tropical Storm Debby centered in the eastern Gulf of Mexico as of 1511Z:
My weekend update on the Atlantic tropics is delayed while another area of interest has materialized in the central tropical Atlantic to the east of the Lesser Antilles... and I am currently formulating a forecast for the new area of interest. Meanwhile I recently finished an updated forecast for Debby which I am releasing in this special update below:
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.
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 11 AM 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. I will be considering an increase in my intensity forecast for Debby for my next full update on the Atlantic tropics to be released later today.
******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)... 85 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
Comentários