Mesoscale Precipitation Discussion 0770
NWS Weather Prediction Center College Park MD
427 AM EDT Wed Sep 05 2018

Areas affected...Central/Southern MS...West-Central to Southern
AL...Far western FL panhandle

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

Valid 050825Z - 051425Z

Summary...Tropical Storm Gordon will continue to cause areas of
flooding and flash flooding. However, the worst of the conditions
should focus over southern AL through the early to mid morning
hours where significant flash flooding concerns will be expected
as very heavy rainfall trains over the same area.

Discussion...The latest radar, satellite and surface observations
indicate Tropical Storm Gordon moving farther inland across
southern MS. The latest GOES-16 WV suite shows a substantial
amount of mid level dry air getting entrained around the southwest
flank of the storms's circulation and this is resulting in the
convective rainfall orientation being completely focused around
the northern and eastern semicircles of the storm.

The heaviest rainfall is associated with the deep southerly
moisture and instability transport axis advancing in off the
northern Gulf of Mexico and across far southern AL. This is where
we have a nose of 2.5 inch PWATS and MLCAPE values of about 2000
j/kg. Strongly convergent low level flow here has been aiding a
well organized band of heavy showers and thunderstorms which has
been training south to north and only very gradually has the band
been shifting west as Gordon's circulation center advances off to
the northwest over southern MS.

Going through 12Z, the latest HRRR guidance strongly supports this
westward shift temporarily stopping which will continue to allow
for a south to north axis of training convection, and with
extremely heavy rainfall rates that could reach over 3 inches/hr.
Numerous runs of the HRRR are favoring as much as 4 to 8 inches of
additional rainfall potential through mid-morning with an emphasis
on southwest to far southern AL and edging again back across the
far western FL panhandle. Significant flooding and flash flooding
concerns will exist over these areas as a result.

Meanwhile, closer to the circulation of Gordon over southern MS,
the airmass is considerably more stable, and the rainfall
advancing up across west-central AL and toward central MS is
generally of a moderate to locally heavy rainfall character at
this time with little in the way of deep convection. Thus,
expecting considerably less rainfall amounts here by comparison,
with additional totals of as much as 2 to 4 inches. Some flooding
concerns here are expected, but again the dominant focus will on
southern AL and the far western FL panhandle at least through
mid-morning where extremely heavy rainfall and significant
concerns for flooding and flash flooding are expected.

Orrison

ATTN...WFO...BMX...JAN...MOB...TAE...

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

LAT...LON   32778947 32698817 32278736 31868706 30958640
            30358631 30278693 30188735 30088800 30298821
            30748817 31048825 31308848 31518876 31568909
            31538937 31478979 31659016 31949036 32489016