022
AWUS01 KWNH 141826
FFGMPD
FLZ000-150025-

Mesoscale Precipitation Discussion 1009
NWS Weather Prediction Center College Park MD
225 PM EDT Sat Sep 14 2024

Areas affected...southeastern coast of FL Peninsula

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

Valid 141825Z - 150025Z

SUMMARY...Thunderstorms will increase in coverage through the
remainder of the afternoon across southern FL. The storms will be
capable of high rainfall rates of 1-2 inches in 15 minutes and
localized totals of 2-4 inches. While these high rates may overlap
the urban southeastern corridor, coverage will not be widespread,
but could still result in localized areas of flash flooding.

DISCUSSION...18Z visible imagery across FL showed thunderstorms
initiating along the sea breeze as well as across portions of the
interior southern FL. The environment characterized by the 12Z MFL
sounding contained 2.2 inches of precipitable water and high
relative humidity throughout the column along with deeper layer
mean flow of about 10 kt. Since then, some drier air was noted on
water vapor imagery and LPW imagery in the 500-300 mb layer,
advancing southeastward across the west coast of FL, likely to
reach southeastern FL by 00Z. The 18Z SPC mesoanalysis showed
roughly 3000 J/kg MLCAPE across southeastern FL with little to no
CIN. In addition, flow in the upper levels was diffluent around an
upstream ridge centered over TX and upper level troughing over the
Southeast, which should broadly aid in ascent across the region.

Expectations are for scattered thunderstorms to continue
developing across southern FL over the next few hours, with a mean
movement from west to east, following the deeper layer mean wind.
A lack of stronger shear should keep cells disorganized and likely
limit residence time over any given location to an hour or two at
maximum. However, the very moist environment and relative slow
movement of cells, combined with outflow and cell interactions,
will result in highly efficient rainfall of 1 to 2 inches in 15
minutes within the stronger cores. Localized rainfall of 2-4
inches will be possible over portions of southeastern FL, from
southern St. Lucie County down to southern Miami-Dade County.
Depending on storm coverage late this afternoon and the arrival of
drier air in the upper levels, increased outflow/forward
propagation could materialize toward the 00Z time frame. While
higher rainfall rates are expected to be hit or miss across the
region, there could be some overlap with the largely impervious
urban corridor, resulting in localized flash flooding through 01Z.

Otto

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

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

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

LAT...LON   27388028 27217998 26817976 26387977 25677988
            25348010 25268040 25338057 25508062 25938052
            26518046 27208044