862
FXUS64 KBRO 011742
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
1242 PM CDT Mon Sep 1 2025

...New DISCUSSION, AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1206 PM CDT Mon Sep 1 2025

-The Weather Prediction Center includes portions of Brooks, Jim
 Hogg, Starr and all of Zapata County within a Marginal Risk
 (level 1 of 4) for excessive rainfall through the rest of today
 and tonight.

-Rain chances increase late tonight into tomorrow afternoon across
 all of deep south Texas and the Rio Grande Valley.

-Dry weather returns Wednesday and unsettled weather is possible
 this weekend.

&&

.DISCUSSION...
Issued at 1206 PM CDT Mon Sep 1 2025

Throughout this evening and into tomorrow afternoon, precipitable
water (PWAT) values are expected to rise to around 1.9-2.3 inches
from north to south across deep south Texas and the Rio Grande
Valley as a frontal boundary gradually drifts southward through the
region, pushed by north-northwesterly mid-level flow. Associated
forcing and convergence will aid in maintaining unsettled weather
for this time frame. There is a low to medium (30-60%) chance of
showers and thunderstorms continuing for several hours beyond
sunset this evening, mainly west of US-281 across portions of the
northern ranchlands (northwestern tip of Brooks and
northern/western half of Jim Hogg counties) and the Rio Grande
Plains (Starr and Zapata counties), where WPC indicates a
Marginal Risk (level 1 of 4) for excessive rainfall. Probabilistic
guidance continues to yield low confidence in rainfall amounts as
forecast QPF varies significantly from as low as around 0.15-0.50
of an inch (NBM mean) to as much as 0.40-1.30 inches (NBM 90th
percentile), with the greatest amounts across portions of the Rio
Grande Plains. Considering the high PWAT values, any developing
convection will be able to produce localized heavy rainfall,
resulting in ponding of water on roadways and low-lying areas.

Throughout tomorrow morning, probabilities increase across the
entire region to a low to medium (30-50%) chance of rain, highest
along and east of I-69 E through late morning, increasing to a
medium to likely (40-70%) chance by the afternoon and early
evening hours, with the greatest chance along and east of
US-281/I-69 C across the lower and middle Rio Grande Valley.
Later in the evening and overnight tomorrow night, a surge of high
pressure, resulting from an enhanced northerly jet over northern-
central Texas, is expected to push the boundary south of the
region, reducing PoP`s to less than 15% late tomorrow evening
through Friday as mid-level ridging regains control, though
isolated convection remains possible across SPI and the lower Rio
Grande Valley Wednesday morning and afternoon. Unsettled weather
is anticipated to return this upcoming weekend as a mid-level
trough passes over the region, bringing a low to medium (30-60%)
chance of rain into the beginning of next week.

Near average high temperatures are expected tomorrow (mid-to-upper
90`s) increasing to slightly above average further inland Wednesday
through Friday (upper 90`s and lower 100`s) as sun clouds clear
before gradually cooling to slightly below average over the weekend
and into next Monday (low to mid 90`s) as clouds build and PoP`s
rise. Mostly minor (level 1 of 4) heat risks tomorrow increase to
mostly a mostly moderate (level 2 of 4) risk, with pockets of
major (level 3 of 4) across the Rio Grande Valley, Wednesday
through Saturday. Heat risks generally become mostly minor
for Sunday and Monday.

&&

.AVIATION...
(18Z TAFS)
Issued at 1206 PM CDT Mon Sep 1 2025

Showers and thunderstorms have been developing throughout this
morning and early afternoon, already bringing rain and
thunder to KBRO. Additional development is possible at KBRO this
afternoon, but more likely at KHRL within the next few hours and
possibly reaching KMFE by the late afternoon and early evening
hours. Otherwise, light and variable winds are expected,
potentially becoming a gentle 5-10 knot easterly breeze later this
afternoon before becoming light and variable, or calm, again
overnight tonight. Late tonight, chances of showers and
thunderstorms return, continuing into tomorrow afternoon as a
frontal boundary arrives. Any convection that develops has the
potential for heavy rain, cloud to ground lightning and gusty
winds.

&&

.MARINE...
Issued at 1206 PM CDT Mon Sep 1 2025

Favorable marine conditions hold as light and variable winds and
slight (1-2 feet) seas continue, becoming gentle to moderate by
Friday and slight to moderate (2-3 feet) seas over the weekend.
Probabilities of showers and thunderstorms increase from north to
south to a medium to high (40-70%) chance by tomorrow morning before
decreasing throughout the afternoon and evening hours down to less
than 15% chance tomorrow night, persisting through the daytime
Friday as high pressure takes over. More unsettled weather is
expected this weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             79  95  78  95 /  30  60  30  20
HARLINGEN               75  95  73  98 /  40  60  10  10
MCALLEN                 79  98  77 101 /  40  60  20  10
RIO GRANDE CITY         77  97  75 101 /  60  50  20  10
SOUTH PADRE ISLAND      81  89  81  89 /  40  50  20  10
BAYVIEW/PORT ISABEL     77  93  77  93 /  40  60  20  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

SHORT TERM...65-Irish
LONG TERM....65-Irish
AVIATION...65-Irish