Tropical Storm Debby Discussion Number  20
NWS National Hurricane Center Miami FL       AL042024
500 AM EDT Wed Aug 07 2024

Debby's circulation consists of a nearly 60 nm wide convection-free
region near the center, which is drifting eastward off the coast of
South Carolina.  Moderate to deep convection is organized in broken
bands well away from the center, with the strongest band currently
feeding into eastern North Carolina.  The storm appears to have
strengthened slightly now that a greater proportion of the
circulation is back over water, and the initial intensity is set at
40 kt based on a 0143 UTC ASCAT-B pass.

The longer-term motion is slowly eastward, or 085/4 kt.  Although
Debby is expected to maintain a slow motion for the next 24 hours or
so, a mid-level ridge over the western and central Atlantic should
cause the storm to turn northward today, with the center reaching
the coast of South Carolina by tonight.  Debby should then
accelerate toward the north and northeast beginning on Thursday over
the eastern United States and eastern Canada, ahead of a deep-layer
trough moving across the Upper Midwest and Great Lakes region.  No
changes were required to the new NHC track forecast, which lies on
top of the previous forecast and down the middle of the guidance
envelope.

Debby's structure does not argue for any type of significant
strengthening, but warm ocean waters of 29 degrees Celsius and low
shear could allow the wind field to strengthen a bit over the next
24 hours while the circulation remains over water.  A peak intensity
of 45 kt is shown at 12 and 24 hours, which is generally in line
with the bulk of the intensity guidance.  Weakening is forecast to
begin by 36 hours once the center moves inland, and global model
fields and phase-space diagrams indicate that Debby is likely to be
absorbed by a front and become extratropical by 60 hours over the
Mid-Atlantic region of the United States.


Key Messages:

1. Heavy rainfall across portions of eastern South Carolina and
southeast North Carolina is expected to persist through Thursday
which would broaden areas of considerable flooding. Expected heavy
rainfall will likely result in considerable flooding impacts from
the Piedmont of the Carolinas, portions of the Mid-Atlantic States,
and Vermont through Saturday morning.

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  07/0900Z 31.9N  79.5W   40 KT  45 MPH
12H  07/1800Z 32.3N  79.3W   45 KT  50 MPH
24H  08/0600Z 32.9N  79.5W   45 KT  50 MPH
36H  08/1800Z 34.1N  79.8W   35 KT  40 MPH...INLAND
48H  09/0600Z 36.0N  79.7W   30 KT  35 MPH...INLAND
60H  09/1800Z 39.2N  77.8W   30 KT  35 MPH...POST-TROP/EXTRATROP
72H  10/0600Z 43.8N  73.9W   30 KT  35 MPH...POST-TROP/EXTRATROP
96H  11/0600Z 50.8N  62.1W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  12/0600Z 53.9N  53.5W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg