886
AWUS01 KWNH 121216
FFGMPD
FLZ000-121800-

Mesoscale Precipitation Discussion 0427
NWS Weather Prediction Center College Park MD
815 AM EDT Wed Jun 12 2024

Areas affected...western (Gulf) coast of central and southern FL

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

Valid 121215Z - 121800Z

Summary...Localized rainfall rates on the order of 2-4"/hr may
support additional localized totals of 6"+ with sufficient
training/repeating of cells. Localized instances of flash flooding
are likely, given the increased sensitivity from recent heavy
rainfall.

Discussion...Heavy shower activity is once again building over the
warm waters of the southeast Gulf of Mexico, following a relative
lull this morning in convective activity along the western coast
of central FL. A 25-35 kt low-level jet (LLJ) is situated just
downstream (with the maxima near the eastern central coast of FL),
resulting in a localized enhancement of lift (via DPVA with
minimal influence from upper-level dynamics). The mesoscale
environment is reminiscent of the tropics, as PWATs of 2.0-2.5"
are near record levels (per TBW sounding climatology) with dew
points in the upper 70s to near 80deg F, ML CAPE of 1000-1500
J/kg, and effective bulk shear near 20 kts. While deep convection
may be able to tap into more significant instability (as indicated
by 3000-5000 MU CAPE just offshore), relatively shallow heavy
showers/thunderstorms will easily produce 1-2"/hr rates (with more
intense convection capable of 2-4"/hr rates, particularly if
additional training/repeating occurs).

Hi-res CAMs paint a rather concerning picture this morning,
suggesting additional localized totals of 6"+ are possible through
18z. This is indicated by both the 06z HREF probability matched
mean (PMM) QPF and 40-km neighborhood exceedance probabilities
(40-70% for 5" exceedance), as well as by hourly runs of the HRRR
since 06z. That said, not every HREF member or every run of the
HRRR indicates such totals, as this threat is conditionally
dependent on a training/repeating axis to set up along the coast.
This could occur anywhere from Sarasota to Naples, though the Fort
Myers/Punta Gorda region looks most favored (per the observational
trends matching up quite well with guidance). Given that average
totals over the past 24 hours commonly range from 3-5" (with
localized totals remarkably as high as 6-12", per MRMS
esitimates), isolated instances of flash flooding appear to be
likely (with locally significant impacts possible in poor
drainage, urbanized terrain).

Churchill

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

ATTN...WFO...MFL...MLB...TBW...

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

LAT...LON   28188232 27958105 26628083 25558114 25978226
            27288306 27968304