Heavy Rain/Flooding SW FL
From
Mike Powell@618:250/1 to
All on Wed Jun 4 07:34:00 2025
AWUS01 KWNH 041201
FFGMPD
FLZ000-041800-
Mesoscale Precipitation Discussion 0359
NWS Weather Prediction Center College Park MD
800 AM EDT Wed Jun 04 2025
Areas affected...southwestern FL
Concerning...Heavy rainfall...Flash flooding possible
Valid 041200Z - 041800Z
Summary...Showers and thunderstorms are increasing in coverage and
intensity offshore, and should start moving ashore shortly.
Hourly rain amounts to 3" with local amounts to 5" are possible,
which would be problematic in urban areas.
Discussion...An upper level low is noted in water vapor imagery in
the northeast Gulf, south of Apalachicola. An area of scattered
thunderstorms have formed offshore southwest FL which is slowly
broadening and intensifying, while an outflow from overnight
convection is approaching the convection's southeastern flank. As
of this discussion's sending, hourly rain estimates are in the
0.5-1" range to the northwest of Captiva. The synoptic surface
wind field is light out to the east to southeast, while flow at
850 hPa is south to southwest at 20-25 kts per VAD wind profiles
and RAP forecasts, bringing effective bulk shear to 25 kts.
Precipitable water values are around 2". ML CAPE values have been
slowly rising along the immediate coast per SPC mesoanalyses,
where skies are mostly clear as of this discussion's sending. For
the moment, CIN is present inland. Offshore ML CAPE values are
1000-1500 J/kg.
Some additional increase in instability is expected before the
showers and thunderstorms move inland. Should the convection
continue increasing in coverage, which is implied by a modest
increase in the Galvez-Davison index to 30 in the 15-18z time
frame and recent radar trends, this would force the instability
gradient to remain rather coastal. Given the effective bulk
shear, some level of convective organization is anticipated, which
should help with increasing hourly rain amounts if convection gets
anchored to a coastal instability gradient, short periods of cell
training, or cell collisions/mergers occur. The mesoscale
guidance has isolated to widely scattered signals for 3-5" totals
between Sarasota and Naples. Given the ingredients present,
hourly rain amounts to 3" with local totals to 5" are possible,
which would be most problematic in urban areas.
Roth
ATTN...WFO...MFL...TBW...
ATTN...RFC...ALR...NWC...
LAT...LON 28028238 27048159 26028146 25848180 26258210
27838286
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