Mesoscale Precipitation Discussion 1433
NWS Weather Prediction Center College Park MD
428 PM EDT Sat Oct 03 2026

Areas affected...portions of the Central Gulf Coast

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

Valid 032027Z - 040227Z

Summary...Showers and thunderstorms have been showing increasing
rainfall efficiency as of late in and near southeast LA.  Hourly
rain amounts to 3" are possible, which would be problematic in
urban areas.

Discussion...Recent radar and satellite trends show a tendency for
more rainfall efficiency as of late as thunderstorms show cooling
cloud tops even if the overall pattern is widely scattered. 
Precipitable water values are 2.25-2.5" per GPS data.  Effective
bulk shear is just shy of 25 kts, with upper level west-southwest
flow countering east-southeast low-level flow to some degree.  ML
CAPE is ~1500 J/kg.  Divergence aloft could be aided both by
supergeostrophic flow over the top of an upper level ridge across
the northern Gulf and a weak shortwave transiting MS.

The mesoscale guidance has a heavy rain signal that shifts from
west to east over time within the MPD area, due to a combination
of the shortwave's movement eastward and recent RAP runs forming a
circulation at 850 hPa which approaches the Mouth of the MS River/
Breton and Chandeleur Sounds towards 06z.  An instability
gradient/convective focus attempts to conform to the coastline as
convection inland exhausts instability ashore while onshore flow
keeps instability around for coastal areas.   Hourly rain amounts
to 3" are possible, given the ingredients available.  This would
be most problematic in urban areas.  Any flash flooding is
expected to be isolated to widely scattered in coverage.

Roth

ATTN...WFO...JAN...LCH...LIX...MOB...TAE...

ATTN...RFC...ALR...ORN...NWC...

LAT...LON   31048754 30888649 30368609 29608730 28988900
            29029078 29499187 30619071 30948935