AWUS01 KWNH 121113
FFGMPD
FLZ000-121600-

Mesoscale Precipitation Discussion 0259
NWS Weather Prediction Center College Park MD
713 AM EDT Mon May 12 2025

Areas affected...South Florida...

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

Valid 121115Z - 121600Z

SUMMARY...Compact MCS with rates of 2.5-3"/hr and some training
elements may result in quick 3-5" totals and rapid inundation
flooding IF collocates with urban areas over next few hours.

DISCUSSION...CIRA LPW and surface observations depict a sharpening moisture/dewpoint gradient along and southeast of Biscayne Bay,
with values in the Sfc-850mb layer near .7" while south across the
FL straits near/over 1-1.1". This is supporting an isentropic boundary/effective warm front developing due to increasing
southwest to southeast 15-25kt confluence along/ahead of NNE to
SSW convective band crossing the central Keys. This allows for an
effective triple point to exist across the Everglades along the Monroe/Miami-Dade county line. The strength of the moisture convergence/confluence and higher surface theta-E air to support
SBCAPEs of 2000-2500 J/kg will support the rapidly cooling CB tops
below -65C. Cells along the effective warm front have sufficient
bulk shear to be rotating increasing moisture flux convergence for
rainfall efficiency to greater than 2.5"/hr. Isolated, narrower
updraft cells will exist along and northeast of the triple point
through the length of the warm conveyor belt that extends north to
just east of Cape Canaveral. Cells will be less efficient within
the broader moderate shield precipitation given reduced available
instability.

There remains great uncertainty in the evolution/track of the MCV
and therefore the triple-point and warm frontal convection.
Dynamically biased Hi-Res CAMs (ARW, Nam-Nest, HRRR, RAP) suggest
a continued northeastward track of the MCV lifting the heavy
rainfall/triple point corridor northeastward across urban
Miami-Dade/Broward. However, thermodynamically biased guidance
(RRFS, ARW2, etc) suggest higher theta-E release in the mid-levels
and increased outflow and forward propagation out across the Gulf
stream east, resulting in a more moderate broad shield
precipitation to occur over the urban corridor. RADAR trends
would support the latter, reducing the overall risk of heaviest
rainfall to the near-offshore from Biscane Bay, eastward, but the
former cannot be fully ruled out. Currently, the greatest risk
appears to be in the Homestead/southern Dade urban areas lifting
northeast toward downtown Miami with spots of 3-5" possible over
the next 1-3 hours.

Gallina

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

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

LAT...LON 26918021 26707996 26068001 25638009 25218026
24968056 25018090 25198112 25668102 26148062
26768049
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