Mesoscale Precipitation Discussion 0753
NWS Weather Prediction Center College Park MD
149 PM EDT Mon Sep 03 2018

Areas affected...South FL & the Keys

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

Valid 031748Z - 032203Z

Summary...Convergent bands of showers and thunderstorms are
expected today around the southeast side of Tropical Storm Gordon.
 Hourly totals to 3" with additional local amounts to 5" are
possible before Gordon pulls away.

Discussion...Tropical Storm Gordon appears to be intensifying near
25.8N 81.7W at this time south of Marco Island with a forming,
partial eye wall/bounded weak echo region apparent near this
location.  Bands of showers and thunderstorms are streaming into
southern FL from the FL Straits.  Inflow at 850 hPa is convergent
at 20-50 kts per VAD wind profiles and 88D velocity information,
nearly double the mean 850-400 hPa wind.  Precipitable water
values are 2.25-2.5".  ML CAPE values appear to be on the rise
within the warm advection portion of the storm in this area, now
500-2000 J/kg.

The expectation is that bands of convection will attempt to drift
northwestward with time, with the mesoscale guidance shows them
exiting South FL around 22z when the low level flow in the wake of
Gordon becomes increasingly anticyclonic.  Until then, hourly rain
totals to 3" are possible.  The mesoscale guidance has a good
signal for local amounts in the 5" range over the next several
hours, which looks realistic.  These amounts would be most
problematic within urban areas.

Roth

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

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

LAT...LON   27608035 26837993 25688000 24898052 24668088
            24418194 24518221 24628221 24768169 24988118
            25258126 25588129 25728152 25908189 26448208
            26988171