MY 2025 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #31

*******Note that forecasts 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... SUNDAY JULY 6 2025 12:15 PM EDT...

Overnight Chantal became better-organized and strengthened briskly as wind shear dropped over the tropical storm... reaching a peak strength of 60 mph maximum sustained winds by the time the center made landfall over northeastern South Carolina between 2 AM and 5 AM EDT. Because thunderstorms had wrapped into the center under reduced shear... this allowed for tropical storm conditions over northeastern South Carolina in addition to southeastern North Carolina. The track has had a westward lean since landfall time due to the blocking surface ridge passing to the north... which is allowing the inland remnant low to drive heavy rainfall (with flash flood potential) across central North Carolina in addition to eastern North Carolina. As the blocking surface ridge continues offshore... the remnant low of Chantal should bend more north then north-northeast in track... shifting the heavy rainfall/ flooding risk zone across central and eastern Virginia... Maryland... and Delaware over the next 24 hours.

...UPDATE... SATURDAY JULY 5 2025 9:35 PM EDT...

The 8 PM EDT center fix of Tropical Storm Chantal (32.3N-78.7W) suggests the surface center is reforming northeast closer to the sheared-off thunderstorm canopy... a position of northeast of the 5 PM EDT NHC forecast track and my forecast track generated earlier in the afternoon... this could explain the southwest-northeast elongation of the low-level cloud swirl noted in the 7:55 PM EDT discussion below which is a symptom of an older southwestern center fading and newer northeastern center developing. Center reformations in sheared tropical cyclones often happen if the sheared-off thunderstorm canopy produces enough latent heat release whose warm core upper anticyclonic outflow drops surface pressures closer to the canopy. The following is an update to the expected impacts given the latest position of Chantal:

(1) A sooner landfall of the center... thus a sooner deterioration of weather conditions across southeastern North Carolina through late tonight and the peak of the severe weather by tomorrow morning instead of tomorrow midday. Expect coastal surf and gusty winds... gusty winds cannot be ruled in inland areas. Heavy rainfall with flash flooding potential is another hazard.

(2) It is possible the center develops new thunderstorm bursts directly overhead by tomorrow morning as the shear over Chantal relaxes... this would allow for gusty winds... coastal surf... and heavy rainfall with flash flooding potential over northeastern South Carolina. The risk of gusty winds and coastal surf is reducing for the central South Carolina coast.

(3) The inland remnant tropical low continues north-northeast across eastern North Carolina and mid-Atlantic United States by later tomorrow through Monday. As such heavy rainfall with flash flooding potential proceeds across eastern North Carolina... eastern Virginia... and as far northeast as southeast Maryland and southern Delaware.

...SATURDAY JULY 5 2025 7:55 PM EDT...

See Tropical Storm Chantal section below for an update on the tropical storm expected to bring impacts to parts of the Carolinas in the next 24 hours.

To the southeast of Chantal and to the north of the northeastern Caribbean Islands... a surface trough of low pressure developed over the last couple of days due to upper divergence on the southeast side of the current western Atlantic upper vorticity string and will continue northwest into the waters southwest of Bermuda while rounding the steering Atlantic surface ridge. Since the formation of the surface trough... the upper vorticity string has split into one upper vortex retrograding southwest into the north coast of Haiti under the force of a growing upper anticyclone over Chantal and a larger upper vortex to the east in the vicinity of 25N-55W. A small upper anticyclone has sprouted in the gap between the two upper vortices and over the surface trough... as a result the surface trough has been able to maintain a small area of thunderstorms thru today. This is likely to continue for the next several hours due to divergence along the leading edge of upper vorticity to the north to be left behind by the current northwest Atlantic upper trough. Eventually the upper vorticity is pushed further south and over the surface trough by the upper ridge exiting the eastern US where it would cap development of the trough... therefore tropical development is unlikely due to the short amount of time before upper winds become unfavorable.

For the low-latitudes of the tropical Atlantic... tropical development between the Lesser Antilles islands and west coast of Africa has been precluded by surges of dry Saharan air. Recent satellite imagery shows the latest surface tropical wave of low pressure emerging from the west coast of Africa is maintaining squalls of thunderstorms to the south of the latest dry air surge. If this continues... this tropical wave may require monitoring for signs of development between Africa and the Lesser Antilles while it continues west... due to an eastern tropical Atlantic upper ridge with low vertical shear and upper outflow that will remain in place.

TROPICAL STORM CHANTAL... The tropical low offshore of the southeastern United States was confirmed by aircraft recon data to be tropical depression three (the third tropical cyclone of the 2025 Atlantic Hurricane Season) as of 5 PM EDT Friday. By 8 AM EDT today another round of aircraft recon data confirmed the depression had strengthened into Tropical Storm Chantal. The tropical cyclone has been quasi-stationary with only a slow northward drift due to a blocking surface ridge over the eastern US... and has the classic appearance of a sheared tropical cyclone with the low-level swirl located west of the thunderstorm canopy. The shear is being imparted by southeastern US upper vorticity that has recently been separated from the upper trough that is now moving into the northwest Atlantic from eastern Canada... due to the force of the current eastern US upper ridge. The entirety of the southeastern US upper vorticity is still forecast to retrograde southwest and away from Chantal and toward Louisiana/ the northwestern Gulf of America... which will promote a reduction in wind shear over Chantal by tomorrow. An outflow enhancing upper anticyclone also expands over Chantal in the increasing gap between the retrograding southeast US upper vorticity and northwest Atlantic upper trough... and the expanse of the favorable upper anticyclone is enforced as the eastern US anticyclonic warm core upper ridge shifts east and overspreads the area in the next 24 hours. Because Chantal's structure has become degraded by the shear as evidenced by the southwest-to-northeast elongation of the low-level cloud swirl... the tropical storm will need some time to recover under the reduced shear and improved upper outflow pattern and therefore I have lowered my intensity forecast (also noting the NHC has progressively raised their intensity forecast and now my forecast is aligned with the NHC's as of this writing). Forecast track is increasingly faster to the north then north-northeast while arcing around the west side of the steering Atlantic surface ridge... especially after the blocking eastern US surface ridge moves offshore and merges with the Atlantic ridge.

Impact to land areas with the current forecast are as follows:

(1) Deteriorating weather conditions for northeastern South Carolina and southeastern North Carolina by midday tomorrow... gusty winds particularly along the central and northeastern South Carolina coast (assuming the thunderstorm distribution and wind field becomes more symmetrical under the reduced shear by 24 hours such that the expanse of the weather reaches the central South Carolina coast)... bouts of gusts cannot be ruled out for inland regions... coastal surf from the central South Carolina coast to the southeastern North Carolina coast... heavy rainfall with flash flooding potential.

(2) The inland remnant tropical low continues north-northeast across North Carolina and mid-Atlantic United States by Monday. As such heavy rainfall with flash flooding potential proceeds across central and eastern North Carolina... central and eastern Virginia... and as far northeast as Maryland and Delaware.

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

0 Hr Position (1800Z Jul 5)... 45 mph maximum sustained wind tropical storm centered offshore of South Carolina at 31.6N-78.7W

IOH 24 Hr Forecast (1800Z Jul 6)... 50 mph maximum sustained wind tropical storm centered on the northeastern South Carolina coast at 33N-79W

IOH 48 Hr Forecast (1800Z Jul 7)... Remnant low centered over northeastern North Carolina at 36N-77.5W

*****National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***********************

Peak Strength (0600Z Jul 6)... 50 mph maximum sustained wind tropical storm centered on the northeastern South Carolina coast at 33N-79.3W

36 Hr Position (0600Z Jul 7)... 30 mph maximum sustained wind dissipating inland remnant low centered over central North Carolina at 35.3N-79W

...COMPUTER MODEL SUMMARY...

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

1200Z (Jul 5) CMC Model Run...

**For Tropical Storm Chantal... moves north-northwest into the central part of the South Carolina coast through 18 hours without additional strengthening... weakens to an inland remnant low over northeastern South Carolina by 30 hours... remnant low continues north then northeast across central North Carolina... southeastern Virginia... southeastern Maryland and Delaware... and then into offshore waters south of Long Islands New York through 72 hours... at this position the remnant low becomes absorbed by developing frontal low to the north by 78 hours

0000Z (Jul 5) ECMWF Model Run...

**For Tropical Storm Chantal... moves north into the central part of the South Carolina coast through 36 hours without additional strengthening... weakens to an inland remnant low over northeastern South Carolina by 42 hours... remnant low continues northeast across eastern North Carolina... SE Virginia coast... then into waters just offshore of the mid-Atlantic United States through 72 hours... while positioned just south of Cape Cod Massachusetts becomes absorbed by developing frontal low to the north by 90 hours

1200Z (Jul 5) GFS Model Run...

**For Tropical Storm Chantal... moves north-northwest into the central part of the South Carolina coast through 18 hours without additional strengthening... weakens to an inland remnant low over central South Carolina by 27 hours... moves northeast into eastern North Carolina through 54 hours where it loses identity to incoming surface front to the northwest

1200Z (Jul 5) NAVGEM Model Run...

**For Tropical Storm Chantal... moves north-northwest into the southern part of the South Carolina coast through 24 hours without additional strengthening... weakens to an inland remnant low over central South Carolina by 36 hours... moves northeast across central North Carolina... eastern Virginia... and southeastern Maryland and Delaware through 66 hours shortly after which time it becomes absorbed by surface front incoming from the northwest