AWUS01 KWNH 170959
FFGMPD
MSZ000-LAZ000-171500-

Mesoscale Precipitation Discussion 0726
NWS Weather Prediction Center College Park MD
559 AM EDT Thu Jul 17 2025

Areas affected...Southeast Louisiana...

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

Valid 171000Z - 171500Z

SUMMARY...Repeating banding features and core of 93L

DISCUSSION...09z surface analysis depicts an elongated wave with
weak center feature near/just east of the northern Chandeleur
Islands, with southwestward arching surface to boundary layer
confluence axis crossing the Bird's Foot toward the KOYE Platform
just south of Terrabonne Bay. Moisture flux convergence and deep
layer moisture values of near 2.5" will support efficient rainfall
production for shallow tropical showers. This confluent band will
set up through the Chandeleur Islands and Plaquemines Parish, with
rates of 2-4"/hr and spots of 4-6" possible; and may result in
rapid inundation flooding. Westward propagation appears limited
through the next 4-6hrs so there is only a very low chance the
band will shift far enough west to intersect eastern portions of urban NOLA.

Further west...
Deep layer steering is very weak though northward elongation of
the system is starting to teeter from northeast toward
north-south. This orientation favors northeasterly bands of
warm/moist advection over the lingering drier slot in the NW
quadrant of the circulation. As such, a surface trough will exist
along this drier axis but act as a repeating focus for these
short-term WAA pulses and enhanced moisture convergence waves.
Conditionally unstable air toward the west of this band will
result in thunderstorm development but given deep layer flow
orthogonal to the band, will propagate south and eastward,
limiting overall duration for any given cell. However, with
repeating development increasing totals along and downstream
across Iberville/Iberia parishes and southward may see a slow
increase in overall totals. Given bayous and vast swampy areas,
rapid rise flooding is unlikely with exception of urban locales
with naturally poor drainage. Some Hi-Res CAMs are very
aggressive in the timing/repeating back-building along the
relatively stationary development band, with spot totals of 5"+,
though more likely spots of 2-4" are likely south of I-10 in
proximity to the Atchafalaya River and US-90 corridor. Rapid
inundation flooding is possible but more likely heaviest rainfall
totals are going to remain offshore over the next 4-6hrs.

Gallina

ATTN...WFO...LCH...LIX...

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

LAT...LON 30739118 30189079 29809043 29869007 30228971
30308942 30188898 29608885 28948912 28649007
28979122 29619178 30349171

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