AWUS01 KWNH 172250
FFGMPD
FLZ000-180400-

Mesoscale Precipitation Discussion 1178
NWS Weather Prediction Center College Park MD
550 PM EST Tue Dec 17 2024

Areas affected...east coast of FL

Concerning...Heavy rainfall...Flash flooding possible

Valid 172248Z - 180400Z

SUMMARY...Localized flash/urban flooding will be possible along
the eastern FL Peninsula over the next few hours. Slow cell
movement and/or training will be capable of 1 to 3 in/hr rainfall
rates which may generate isolated excess runoff within the urban
corridor.

DISCUSSION...Radar imagery from KMLB and infrared satellite
imagery through 2230Z showed scattered thunderstorms occurring
along the east coast of FL between Cape Canaveral and Port Saint
Lucie, streaming in from the east following the mean low to
mid-level easterly flow between 10-20 kt. Surface dewpoints in the
lower 70s have contributed to anomalous mid-December moisture with
precipitable water values between 1.5 and 1.8 inches (90th
percentile) with 1500-2000 J/kg MLCAPE observed on the 22Z SPC
mesoanalysis.

Cells were located just north of a weak mid-upper level vorticity
max observed on water vapor imagery over south-central FL, along a
persistent west-east convergence axis seen in fading visible
imagery offshore of the east coast. Mean easterly winds in the low
to mid-levels have supported repeating cells with short-term
training, with observed rainfall rates of 1-2 in/hr near Vero
Beach. While recent cloud top cooling on satellite imagery has
appeared to migrate generally just offshore, redevelopment and
westward translation of heavy rain looks to continue a short-term
urban/flash flood threat from southern Brevard County into St.
Lucie County along the coast where an additional 2-4 inches will
be possible on a highly localized basis through ~01Z.

Indications are that these cells will weaken after 00Z as boundary
layer stabilization occurs with nocturnal cooling, with cells
shifting more offshore or perhaps dissipating. While the HRRR
hasn't been doing well with the ongoing placement of cells, there
are indications in recent HRRR guidance that the activity could
refocus a bit farther south sometime in the 00-03Z time frame.
Similar potential for slow movement and/or training will exist is
development does get going farther south later tonight. Any areas
of flash flooding are expected to remain localized with potential
for a quick 2-4 inches over the next few hours.

Otto

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!5Q_aGikNvzafCzBZkLacufk8V7gRB8rgpd-NiBBSPYDk2FeZhieib_YkAuz--L98hVCe=
yJGOyht5Bs8lDtVQwfvAzcU$  for graphic product...

ATTN...WFO...MFL...MLB...

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

LAT...LON   28308046 27768008 26657985 26118002 26178029=20
            26258043 26628045 27058049 27558065 28018077=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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