AWUS01 KWNH 071600
FFGMPD
NCZ000-SCZ000-072100-
Mesoscale Precipitation Discussion 0826
NWS Weather Prediction Center College Park MD
1159 AM EDT Wed Aug 07 2024
Areas affected...Coastal Plains of North Carolina and northern
South Carolina
Concerning...Heavy rainfall...Flash flooding possible
Valid 071558Z - 072100Z
Summary...Spiral rain bands around Tropical Storm Debby will
periodically pivot onshore through the evening. Rainfall rates
within these bands will likely reach 2-3"/hr at times, resulting
in corridors of 2-4" of rain through training. Flash flooding is
possible.
Discussion...Tropical Storm Debby is clearly evident on GOES-E
visible imagery this morning drifting slowly off of the South
Carolina coast. Although significant dry air has worked in towards
the center of Debby, GOES-E WV imagery shows a channel of
extremely moist air noted as well by CIRA experimental sfc-850mb
PW above the 99th percentile. Within this plume of higher
moisture, which has PWs measured by recent NUCAPS satellite
soundings of around 2.5 inches, bands of rainfall have intensified
and are streaming N/NW around Debby. Although they have generally
struggled to advect onshore due to modest instability noted via
the SPC RAP analysis of 500-1000 J/kg, a steady increase in the
last 3 hours of this MLCAPE is allowing for more widespread
coverage of stronger reflectivity to spread onshore. Recent
radar-estimated rain rates from KMHX WSR-88D have reached as high
as 1.5"/hr, leading to a few pockets of 1-2" of rain in the last 3
hours according to MRMS.
Confidence in the evolution the next several hours is somewhat
uncertain due to how poorly organized Debby looks right now, but
the CAMs do indicate that convection should continue to stream
onshore within the pivoting bands, and eventually expand onshore.
This is supported not only by the CAMs simulated reflectivity, but
also by the ingredients as PWs rise to nearly 2.75" this aftn in
conjunction with increasing destabilization. The placement of any
given band is challenging to identify even at short time scales,
but intense rain rates of 2"/hr (HREF neighborhood probabilities
30-40%) or more (HRRR 15-min accumulations as much as 0.75")
within any of these bands could cause flash flood instances,
especially within any more pronounced training where 2-4" of rain
is likely. The potential for flash flooding will be most likely
across urban areas or where soils are fully saturated (NASA SPoRT
0-10cm RSM above 98%) from recent heavy rains associated with
Debby.
Additionally, although confidence is a bit lower, a more
consolidated region of heavy rainfall may develop just west of the
broad center of Debby along a surface trough and where an
instability gradient is progged to sharpen. If this occurs, more
continuous moderate to heavy rain rates could train N to S,
potentially across the Pee Dee or Lowcounty where rainfall has
already been significant. If this occurs, it could enhance the
flash flood threat across this area as well, separate from the
spiral bands pivoting onshore to the north.
Weiss
...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7xeeE6HMIrK7BX5NUOs-TbjRIZXXiZhEveQPf29CRUBbtQ01CtgbyVtSXBMYSWn2ZBIl=
5fTpHGA90MJQyWKXJOuoT74$ for graphic product...
ATTN...WFO...AKQ...CAE...CHS...ILM...MHX...RAH...
ATTN...RFC...SERFC...NWC...
LAT...LON 36177600 36007558 35577537 35127557 34447677=20
33857795 33687866 33417905 33237933 32917982=20
32958011 33298031 33708034 34088011 34377969=20
34687914 35237840 35637753 36027673=20
=3D =3D =3D
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