358
AWUS01 KWNH 132051
FFGMPD
FLZ000-140200-

Mesoscale Precipitation Discussion 0432
NWS Weather Prediction Center College Park MD
450 PM EDT Thu Jun 13 2024

Areas affected...South Florida and the Florida Keys

Concerning...Heavy rainfall...Flash flooding likely

Valid 132050Z - 140200Z

SUMMARY...A significant and locally life-threatening concern for
flash flooding will continue across South Florida going into the
evening hours as slow-moving showers and thunderstorms with
extreme rainfall rates gradually cross the region.

DISCUSSION...The latest GOES-E IR satellite imagery coupled with
dual-pol radar shows an elongated band of deep convection with
extremely heavy rainfall rates once again gradually settling
southeastward across southern Florida. The coldest cloud tops
within the convective band are still generally offshore over the
southeast Gulf of Mexico where the stronger instability and
moisture convergence has been focused, but some convective tops to
about -65C have been occasionally occurring with the stronger
convective cells that are seen crossing through the Florida
Everglades, and also where MRMS data has been showing some
rainfall rates of 1 to 3 inches/hour over the last couple of hours.

MLCAPE values over southern Florida have risen to 1500 to 2500
J/kg, with a convergent southwest low-level jet of 20 to 30 kts in
place. This is evidenced by the special 18Z MFL RAOB which also
showed a PW of 2.41 inches and a very deep warm/moist column with
the WBZ level up near 550mb or about 510 dm in height.

The thermodynamic environment through the vertical column over
southern Florida is highly conducive for extreme rainfall rates
given the depth of tropical moisture and degree of instability,
and the convective band settling southeast over the next few hours
will be capable of producing 1 to 3 inch/hour rates, with isolated
heavier rates perhaps to around 4 inches/hour with the strongest
of cells. This is supported by the 12Z HREF guidance.

Additional rainfall totals over the next few hours are expected to
reach 4 to 6 inches with isolated heavier amounts not out of the
question as the approaching convective band crosses the region,
including the I-95 urban corridor from Boca Raton and Fort
Lauderdale down through Miami. The convection will also gradually
make it into far southeast Florida (i.e. Homestead) and into the
Florida Keys by mid-evening impacting places such as Marathon and
Key West with similar rainfall amounts expected.

This evening`s axis of heavy rainfall overall should tend to be a
bit more progressive compared to yesterday`s extreme rainfall
event, but given such high sensitivities on the ground and
lingering impacts from multiple days of extreme rainfall with
multi-day totals over southern Florida locally of 15 to 25 inches,
the additional rains heading through early this evening are very
likely to exacerbate ongoing flooding/runoff problems and promote
additional significant urban flash flooding concerns.

Orrison

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

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

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

LAT...LON   26548048 26477996 25548009 24738069 24388171
            24558205 24868132 25048120 25218119 25538124
            25738135 25938128 26258097