698
FXUS64 KBRO 300532 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1232 AM CDT Wed Sep 30 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1230 AM CDT Wed Sep 30 2026

 - Widespread Major (level 3 of 4) to Extreme (level 4 of 4) Heat
   Risk expected across the region through Thursday.

 - Confidence is increasing on a significant weather pattern
   change towards cooler and wetter conditions later this week;
   this includes a multi-day heavy rain and flash flood potential
   Thursday into the weekend.

 - The Weather Prediction Center (WPC) has Deep South Texas under
   a Slight (level 2 of 4) to Moderate (level 3 of 4) Risk for
   Excessive Rainfall for Thursday, and a Marginal (level 1 of 4)
   to Slight Risk Friday and Saturday.

&&

.DISCUSSION...
Issued at 1059 PM CDT Tue Sep 29 2026

An upper level trough over the Southwest will move eastward with
an accompanying cold front forecast to push into Central Texas
Wednesday, before likely stalling Thursday. The front will likely
resume its southeastward movement Thursday night, moving through
Deep South Texas Friday into Saturday morning.

Ahead of the front, southeasterly surface flow will continue to
advect warm moist air into Deep South Texas. This combination of
humidity and hot temperatures will likely continue to produce
afternoon heat index values ranging from 108 to 115 degrees
Wednesday and Thursday. Heat Advisories or Special Weather
Statements will likely be needed for portions of Deep South Texas
Wednesday and Thursday.

The additional moisture will also help raise PWAT values to 2-2.6
inches across Deep South Texas Thursday afternoon into the
weekend. Combined with increased forcing across the area, and some
instability Thursday and Friday, this setup could support some
strong to severe thunderstorms and heavy rainfall Thursday
afternoon through Friday morning. Probabilistic models continue to
support 48 hour rainfall accumulations from 7 AM Thursday through
7 AM Saturday generally ranging from 1-3 inches with locally
higher amounts up to 4 inches possible. The heaviest rainfall is
most likely to occur over Zapata, Starr, Jim Hogg, and portions of
Brooks counties, however there is still some uncertainty in the
track of the storms, and the forecast may shift over the coming
days. This heavy rainfall could result in flash flooding,
especially in low lying or flood prone ares. The hilly terrain in
portions of Zapata and Starr counties could be especially
susceptible to flash flooding.

The Storm Prediction Center has a Marginal Risk (level 1 of 5)
for Severe weather along and west of I-69C Thursday and Thursday
night. The Weather Prediction Center has Zapata and western
portions of Jim Hogg and Starr counties in a Moderate Risk (level
3 of 4) of Excessive Rainfall and the rest of Deep South Texas in
a Slight Risk (level 12of 4) for Excessive Rainfall Thursday.
Zapata, Starr, Jim Hogg and western portions of Brooks counties
remain under a Slight Risk for Excessive Rainfall with the rest of
Deep South Texas under a Marginal Risk (level 1 of 4) for
Excessive Rainfall Friday.

Behind the front, the risk for severe thunderstorms and damaging
wind decreases, however widespread rain chances will continue
through the weekend, with rain generally light to moderate, though
some heavier bands will remain possible. Given the anticipated
rainfall from the preceding days, minor flooding will likely
continue to be a concern over the weekend.

&&

.AVIATION...
(06Z TAFS)
Issued at 1230 AM CDT Wed Sep 30 2026

MVFR to VFR will prevail at the aerodromes through the next 24
hours, with moderate to breezy winds and generally partly cloudy
skies.

&&

.MARINE...
Issued at 1059 PM CDT Tue Sep 29 2026

Winds and seas along the Lower Texas Coast are forecast to
continue increasing Wednesday and Thursday as pressure gradients
tighten ahead of an approaching cold front. Adverse to hazardous
conditions will be possible through Thursday night, and Small
Craft Should Exercise Caution headlines or Small Craft Advisories
may be needed.

The cold front is forecast to move through the area Friday, with
light northeasterly winds behind the front supporting lower seas
through the weekend. Winds and seas may increase again early next
week, with additional Small Craft Advisories possible Monday.

Rain chances are forecast to increase Thursday afternoon, with
widespread rainfall likely through the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             97  83  97  81 /  10  10  30  50
HARLINGEN              100  80 100  76 /   0  10  50  50
MCALLEN                103  83 102  80 /   0  10  60  70
RIO GRANDE CITY        104  81 102  77 /   0  20  60  90
SOUTH PADRE ISLAND      90  84  90  83 /  10  20  20  40
BAYVIEW/PORT ISABEL     96  81  96  79 /  10  10  30  40

&&

.BRO WATCHES/WARNINGS/ADVISORIES...None.

&&

$$