008
AWUS01 KWNH 121751
FFGMPD
FLZ000-122330-

Mesoscale Precipitation Discussion 0428
NWS Weather Prediction Center College Park MD
151 PM EDT Wed Jun 12 2024

Areas affected...South FL into the Upper FL Keys

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

Valid 121750Z - 122330Z

Summary...Rainfall rates of 1-3"/hr to continue across already
soaked regions of South FL, producing additional localized totals
of 5"+. Isolated to scattered instances of flash flooding likely
(some locally significant).

Discussion...A convective complex has gradually organized over the
past several hours over South FL, most evidently identified via
GOES-East with the emergence and expansion of very cold IR cloud
tops (reaching -80deg C). This deep convective activity (with 30
dBZ echo tops indicated to be as high as 50k ft with the strongest
updrafts) has produced impressive estimated hourly totals of 3-4"
(per MRMS), though the highest totals are likely closer to 3"
(given that MRMS has demonstrated a bit of a high bias over the
past several hours, compared to local gauges). Even still,
convection is expected to remain organized given ample instability
(1000-3000 J/kg of ML CAPE), highly anomalous tropospheric
moisture (with PWATs 2.4-2.8", near all-time records at the top of
the range), and impressive effective bulk shear of 25-35 kts (near
the 90th percentile, per MFL sounding climatology). Strong
low-level moisture transport and convergence from the southwest
should allow for continued convective development and maintenance
with training/repeating of 1-3"/hr rates most favored from near
Naples eastward along Alligator Alley/Tamiami Trail to the greater
Miami metro.

Hi-res CAMs have done reasonably well over the past 6 hours, given
that estimated totals reached 6"+ over portions of South FL
(though a bit farther inland than many CAMs anticipated, a result
of deep convective activity growing into a more organized
complex). Concerns for the next 6 hours exist across many of the
same metro areas along the southwest FL coast, but increasingly
concerns are also growing over southeast FL (i.e. greater Miami
metro area), as some of the most impressive convection is poised
to propagate towards the SSE (following the upwind propagation
vector, eventually shifting into the Upper FL Keys as well). The
CAM signals for additional significant accumulations remain
strong, with the 12z HREF probability matched mean (PMM)
indicating localized totals of 6"+, and 40-km neighborhood
probabilities for 5" exceedance of 30-60%. Additional isolated to
scattered instances of flash flooding are likely (especially given
relatively widespread prior 24-hr totals of 3-7"). Some instances
of flash flooding (particularly in poor drainage, urbanized
terrain) may be locally significant.

Churchill

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

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

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

LAT...LON   27418054 27017986 26057975 25078029 25008118
            25628197 26808239