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

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

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

LAT...LON 28188232 27958105 26628083 25558114 25978226
27288306 27968304
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AWUS01 KWNH 130936
FFGMPD
FLZ000-131535-

Mesoscale Precipitation Discussion 0430
NWS Weather Prediction Center College Park MD
536 AM EDT Thu Jun 13 2024

Areas affected...south-central FL Peninsula

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

Valid 130935Z - 131535Z

SUMMARY...Locally heavy rainfall is expected over portions of the
south-central FL Peninsula through 15Z. While the coverage of
heavy rainfall is not expected to be widespread, flash flooding
from rainfall rates of over 1 inch in 15 minutes and/or over 3
in/hr will be possible.

DISCUSSION...Local radar imagery from KTBW and GOES East infrared
satellite imagery showed locally heavy rain occurring via warm
topped showers in the vicinity of Tampa Bay at 09Z. These showers
were focused ahead of a weak mesolow to the southwest of SRQ,
steadily approaching the coast where uninhibited instability of
~1500 J/kg MLCAPE was present via the 09Z SPC mesoanalysis.
Convective inhibition increased with inland extent from the Sun
Coast, especially to the north and south which may act to inhibit
farther spreading of heavy rainfall activity in the short term.

A tropical airmass was in place over central to southern FL with
precipitable water values that ranged from 1.8 inches near Tampa
Bay to 2.5 inches over the FL Keys (per satellite derived TPW
imagery). Due to the dominance of warm rain processes, efficient
rainfall production will be capable of high rainfall rates with
1-2 in/hr likely but even greater subhourly rates rainfall of 1+
inches in 15 minutes possible. As the mesolow continues toward the
NE, a short term flash flood threat will exist with increasing
showers and locally intense rainfall rates.

Farther south, an increase in showers and thunderstorms is
expected to occur later this morning, to the southwest of a
broader 850 mb low estimated to be near 30N 80W via LPW imagery.
An axis of low level convergence (which extends up through 850 mb)
was located south of the broader cyclonic circulation east of the
northern FL Peninsula into the eastern Gulf of Mexico. This low
level convergence axis, aided by increasing 825 mb winds per RAP
forecasts, is likely to become a focus for the development of
locally heavy rain into the mid-morning hours, beginning between
11-13Z with increased surface heating. Rainfall rates of 1-2 in/hr
but with subhourly rainfall of 1+ inches in 15 minutes will be
possible atop very wet antecedent conditions due to 4 to 10+
inches of rain which impacted the south-central FL Peninsula over
the past 48 hours.

Otto

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

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

LAT...LON 28298069 27998035 27608014 26897988 26558023
26038140 26108212 26628252 27318301 27768301
28028283 28128232 28168174
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