Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Aug 06 2024 05:23:21

AWUS01 KWNH 060523
FFGMPD
SCZ000-GAZ000-061120-

Mesoscale Precipitation Discussion 0816
NWS Weather Prediction Center College Park MD
122 AM EDT Tue Aug 06 2024

Areas affected...portions of southeastern GA...southern SC

Concerning...Heavy rainfall...Flash flooding likely

Valid 060520Z - 061120Z

Summary...Tropical downpours with 1-3"/hr rainfall rates to
continue, resulting in additional 6-hourly totals of 4-8" due to
slowing storm motion. Numerous to widespread instances of flash
flooding are likely (with locally catastrophic impacts expected).

Discussion...Tropical Storm Debby continues to slow to a crawl
near the coast of GA early this morning, bringing torrential
rainfall to portions of the Southeast (mainly concentrated to the
north and east of the storms center). Over the past 6 hours alone,
portions of southeastern GA and southern SC have picked up 3-5" of
rain, and even higher totals of rainfall are anticipated over the
next 6 hours. These impressive short-term totals are the result of
extremely efficient tropical downpours, ranging from 1-3"/hr
across a rather broad (100+ mile) stretch of coastline. As the
forward speed of the storm continues to slow (as ridging builds
from the North Atlantic with the departure of a shortwave trough
to the east), these 1-3"/hr rainfall rates will continue over many
of the same localities, fueled by near record levels of
tropospheric moisture (precipitable water values of 2.5-2.8
inches, rivaling the all-time records per CHS sounding
climatology).

Hi-res guidance suggests that flooding impacts will worsen rather
significantly through the morning hours for a good portion of
southeast GA and southern SC, including the metropolitan areas of
Savannah and Charleston. The 00z HREF probability-matched mean QPF
suggests localized totals of 5-10" through 12z, which corresponds
with 40-km neighborhood probabilities for 5" exceedance of 50-80%.
Considering that the 100-yr ARI (average recurrence interval)
threshold is near 7", these exceedance probabilities reach as high
as 50% (centered near Beaufort), suggesting historically
significant amounts of rainfall (which will likely translate to
locally catastrophic flash flooding). Individual runs of the HRRR
since 00z also depict similar QPF, though some runs limit
localized totals to 3-6" (which is similar to the driest members
of the HREF). This "best case scenario" would still easily exceed
6-hr Flash Flood Guidance of ~3.0", so numerous to widespread
instances of flash flooding are likely (and locally catastrophic
flooding impacts are also expected).

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6OwLbRj7rQpcPjxy3HNXs9zpbG0ahMtgaKNl4exayUF6sz_P3BOklJRanERFROPqlMfM=
_Y8ZJk80WgAlsB0D6wRCRhM$  for graphic product...

ATTN...WFO...CAE...CHS...FFC...ILM...

ATTN...RFC...SERFC...NWC...

LAT...LON   33548089 33478011 33287948 32837903 32088016=20
            31688095 31988130 32288199 32868202 33298160=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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