From Mike Powell@454:1/105 to All on Thursday, October 12, 2023 08:20:00
AWUS01 KWNH 120929
FFGMPD
FLZ000-GAZ000-121525-
Mesoscale Precipitation Discussion 1144
NWS Weather Prediction Center College Park MD
528 AM EDT Thu Oct 12 2023
Areas affected...northern FL into southeastern GA
Concerning...Heavy rainfall...Flash flooding possible
Valid 120925Z - 121525Z
Summary...A localized flash flood threat will continue early this
morning for portions of northern FL into southeastern GA from
training rainfall rates of 1 to 3+ in/hr. Additional rainfall
totals through 15Z of 3 to 6 inches may occur.
Discussion...09Z surface observations showed a warm front just
north of AAF and CTY, with a 5-7 degree rise in surface dewpoint
observed between 07-08Z. Regional radar imagery showed mainly
stratiform rainfall north of the warm front with stronger and
increasingly discrete cells near and south of the warm front.
MLCAPE was estimated to be 500 to 1000+ J/kg along and south of
the warm front with a sharp dropoff in instability north of the
front per 09Z SPC mesoanalysis data. A surface low was analyzed
~50 miles south of PNS with a cold front extending SW from the
surface low into the central Gulf of Mexico along with a
pre-frontal convergence axis extending SW from near Panama City.
Strong moisture flux from the south was occurring ahead of the
cold front with nearly 50 kt of 850 mb flow observed on the TLH
VAD wind and PWATs likely over 2.5 inches along the Forgotten
Coast and into portions of the northern Peninsula via recent SPC
mesoanalysis data.
With the exception of an area of cell training just southeast of
Panama City at 09Z, hourly rainfall rates have decreased in
overall coverage and magnitude since 06Z over northern FL. It
appears this lull will be temporary however, with short term
forecasts from the RAP indicating the surface warm front will
continue to lift north through 12Z, becoming oriented favorably to
the mean steering flow from the SW. As the surface low and warm
front lifts north, the rapid rise in low level moisture following
the warm frontal passage will coincide with an increase in
instability supporting the potential for very high rainfall rates
with peak rates of 1 to 3+ in/hr. Continued strong moisture
transport and convergence along the warm front is expected to
support areas of cell training with a focus for the heaviest rain
possibly focusing from northeastern FL into southeastern GA where
multiple rounds of more discrete cells to the south join with
convection near and just north of the warm front. The potential
for additional rainfall totals of 3-6 inches will remain over the
region although these higher end values are likely to remain
localized. A flash flood threat will continue through 15Z,
especially across urban locations or low lying areas of poor
drainage.