Tropical Storm Debby Discussion Number  19
NWS National Hurricane Center Miami FL       AL042024
1100 PM EDT Tue Aug 06 2024

Surface, satellite, and radar observations indicate that the
center of Debby has emerged over the Atlantic southeast of
Savannah, Georgia.  The system is currently comprised of a large
swirl of shallow to moderate convection with occasional patches of
deep convection, particularly in bands to the east of the center.
GOES-16 airmass imagery indicates that interaction with an
upper-level trough has spread cool/dry air aloft over the low-level
center, making the cyclone look somewhat subtropical.  The initial
intensity is held at 35 kt based on Doppler radar winds in the
bands east of the center and a recent 1-minute wind of 31 kt at
NOAA buoy 41008 to the southwest of the center.

Dolly is moving slowly and somewhat erratically eastward, with the
initial motion of 090/4.  The track guidance continues to show a
generally eastward motion for the next 12-18 h, taking the center a
little farther away from the coast.  After that, a building
mid-level ridge should cause the system to turn northward and move
back inland between 24-36 h.  Subsequently, Debby is likely to
accelerate northward and northeastward over the eastern and
northeastern U.S. on the east side of an approaching
mid-latitude trough.  The new forecast track has been adjusted a
little to the left of the previous track through 48 h to better
match the consensus models, and it has been adjusted to the right
during the extratropical phase to better match the global model
guidance.

The dry air aloft, the lack of an inner wind core, and the lack of
deep convection suggest that Debby is at best going to strengthen
slowly, and this scenario is supported by the majority of the
intensity forecast guidance.  The new intensity forecast calls for
gradual strengthening until the cyclone makes landfall between the 
24 and 36 h forecast points.  Weakening is expected after landfall, 
with Debby expected to become post-tropical around 72 h and 
complete transition to an extratropical cyclone by 96 h. The new 
intensity forecast is at the high end of the intensity guidance 
through 36 h and near the intensity consensus after that.


Key Messages:

1. Potentially historic heavy rainfall across portions of eastern 
South Carolina through Friday will likely result in areas of 
catastrophic flooding. Heavy rainfall will likely result in 
considerable flooding impacts from central to the Upstate of South 
Carolina, western North Carolina, Southwest Virginia through 
portions of Mid-Atlantic States, western and northern New York State 
and northern New England through Saturday. 

2. Tropical storm conditions will spread northward along the
southeast U.S. coast from South Carolina to North Carolina through 
Thursday.  Tropical storm warnings and watches are in effect
for portions of that area.

3. A dangerous storm surge is possible along the coast of South
Carolina and southeastern North Carolina from South Santee River to
Cape Fear.  Residents in that area should follow any advice given by
local officials.


FORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 31.8N  80.2W   35 KT  40 MPH
12H  07/1200Z 32.0N  79.6W   40 KT  45 MPH
24H  08/0000Z 32.6N  79.5W   45 KT  50 MPH
36H  08/1200Z 33.4N  79.7W   45 KT  50 MPH...INLAND
48H  09/0000Z 34.7N  79.9W   35 KT  40 MPH...INLAND
60H  09/1200Z 36.9N  79.4W   30 KT  35 MPH...INLAND
72H  10/0000Z 39.9N  77.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
96H  11/0000Z 47.1N  69.5W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  12/0000Z 51.5N  61.0W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven