969
AWUS01 KWNH 121917
FFGMPD
FLZ000-130115-

Mesoscale Precipitation Discussion 1102
NWS Weather Prediction Center College Park MD
315 PM EDT Sat Oct 12 2024

Areas affected...South FL and the Keys

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

Valid 121915Z - 130115Z

SUMMARY...Slow-moving bands of very heavy showers and
thunderstorms are expected to overspread portions of especially
southeast FL and the middle and upper FL Keys going through the
remainder of the afternoon and evening hours. Some urban flash
flooding will be possible.

DISCUSSION...The latest GOES-E IR satellite imagery in conjunction
with dual-pol radar is showing a gradual increase in very heavy
shower and thunderstorm activity across the FL Straits which has
been gradually lifting north-northeastward over the last few
hours. A subtle/weak mid-level shortwave impulse is seen
approaching the region and this energy coupled with the
interaction with an inverted surface trough near the southeast
coast of the FL Peninsula has been facilitating the development of
some semi-organized bands of deeper convection.

There has been an uptick in instability across far southern FL and
in the upper portions of the Keys where MLCAPE values have risen
to 500 to 1000 J/kg. An increase in low-level moisture convergence
has been noted as well close to the coast, and this coupled with
the aforementioned shortwave energy/deeper layer ascent and
proximity of 30 to 40 kts of effective bulk shear should tend to
maintain a threat for relatively organized bands or clusters of
heavy showers and thunderstorms going at least into the evening
hours.

PWs are close to 2 inches and have been tending to rise throughout
the day, and this coupled with the shear and instability should
help drive some very efficient convection with high rainfall rates
that may reach 1.5 to 2.5 inches/hour.

The heavier rainfall threat should tend to overall stay over the
Keys and coastal areas of southeast FL where the better
instability is, but some of these bands of heavy showers and
thunderstorms may impact some of the urbanized I-95 corridor of
southeast FL including Fort Lauderdale and Miami, and also Rt. 1
down through Homestead.

Rainfall amounts of 3 to 5 inches cannot be ruled out in the
middle and upper FL Keys, with the urbanized areas of southeast FL
farther north seeing 2 to 4 inches. If any training of these
slow-moving bands of convection can occur, it will be possible for
locally heavier totals. These rains are expected to drive a threat
for some urban flash flooding.

Orrison

...Please see www.wpc.ncep.noaa.gov for graphic product...

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

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

LAT...LON   26667994 26028000 25388020 24728061 24668118
            24898128 25228098 25838059 26608025