Mesoscale Precipitation Discussion 0750
NWS Weather Prediction Center College Park MD
1003 AM EDT Mon Sep 03 2018

Areas affected...South Florida

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

Valid 031240Z - 031800Z

Summary...T.S. Gordan will likely bring an increasing theat for
heavy rains and localized runoff concerns through the morning
hours.

Discussion...At 12 UTC, NHC indicated newly upgraded T.S. Gordan
has moved into the vicinity of the Middle Keys.  KAMX radar is
showing banded precipitation that is associated with increasing
easterly flow north of center moving onshore across the Upper Keys
and into the southern Florida peninsula.  Radar estimates are
showing rainfall rates of 1 to 1.5 inches/hr associated with some
of these heavier rainbands.   GOES-16 IR imagery is also showing a
broad area of cooling cloud tops east of the center.  The most
recent SPC mesoanalysis is showing PWs of 2 to 2.4 inches across
much of South Florida with 20-30 kt inflow at 850mb.  Although
Gordon is expected to move steadily to the west, strong
southeasterly to easterly flow east of the center is expected to
support deep moisture transport into the region, with the latest
RAP continuing to show the potential for back-building bands --
raising the threat for heavy amounts through the morning into the
early afternoon hours.  For the 6-hr period ending at 18 UTC,
deterministic amounts from recent runs of the HRRR as well as the
00 UTC runs of the HRW-ARW/NMMB and the 06 UTC NAM Conest all show
the potential for 2 to 4 inches, with locally heavier amounts
within the highlighted region.  HREF 40 km neighborhood
probabilities are 50 percent or greater for amounts of 2 inches or
more for much of the region.  These amounts may cause localized
runoff concerns, especially across urbanized and poor drainage
areas.

Pereira     

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

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

LAT...LON   27148033 26537998 25828008 25168041 25158115
            25818123 26528059