AWUS01 KWNH 072316
FFGMPD
FLZ000-080500-

Mesoscale Precipitation Discussion 1094
NWS Weather Prediction Center College Park MD
716 PM EDT Mon Oct 07 2024

Areas affected...southern FL into the Keys

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

Valid 072314Z - 080500Z

Summary...There is potential for a training axis of heavy rain to
begin to impact portions of the southern FL Peninsula into the FL
Keys by 03-06Z. Rainfall rates of 2 to 3+ in/hr will be possible,
which may lead to flash flooding over impervious surfaces.

Discussion...23Z surface observations, radar imagery and fading
visible satellite imagery showed a quasi-stationary front
extending east to west across the southern FL Peninsula with an
apparent low on the front or at least the front aloft, located
north of Grand Bahama Island. A secondary smaller low was noted
just east of the Martin/Palm Beach County border, possibly
connected to the front at the surface or just aloft.

Low level easterly flow just north of the smaller low near the
east coast of FL was helping to support locally heavy rain near
and just east/offshore of Port Saint Lucie where a small bubble of
500 J/kg MLCAPE was estimated via the 22Z SPC mesoanalysis. The
coastal circulation may translate southward in the short term as
the larger low to the north of Grand Bahama is forecast by short
term RAP guidance to strengthen and become better organized
tonight. This strengthening should result in increased northerly
flow over the southern FL Peninsula, pushing the front southward
toward the Middle and Upper Keys by 06Z. Farther southward
progress of the front will likely be limited by southwesterly flow
to the east of yet another surface low analyzed in the eastern
Gulf near 26.4N 84.4W.

The front is expected to act as a focus for the development of
heavy rain where MLCAPE is forecast to be 1000+ J/kg along and
south of the boundary, dropping off to less than 100 J/kg to the
north. Mean steering flow should be roughly parallel to the
boundary allowing for the repeating and training of cells, with
rainfall rates possibly reaching 2 to 3+ in/hr within the tropical
environment. These rates could overlap with localized urban
centers and related impervious surfaces of the Middle/Upper Keys
leading to localized flash flooding.

Regarding the HRRR, while it has been fairly consistent with the
idea of an axis of heavy rain developing in the vicinity of
Florida Bay, the HRRR has struggled with placement of heavy rain
from earlier today and has had differences in its forecast
placement of the surface front and associated low pressure centers
leading to lower confidence in its output. While the idea of
recent HRRR cycles seems reasonable, some of its runs with 6 hr
QPF maxima of 7 to 10 inches appears overdone.

Otto

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

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

LAT...LON   27508019 27488009 27367996 27277992 27017985 
            26607975 25927983 25387993 24768044 24468117 
            24508196 25668170 25798099 26208030 26878038 
            27248040 27418036 
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