textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1235 AM CDT Tue Sep 29 2026

- Widespread Major (Level 3 out of 4) heat risk with pockets of Extreme (Level 4 of 4) Heat Risk to continue 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 all of Deep South Texas under a Slight (Level 2 of 4) Risk for Excessive Rainfall for Thursday, and a Marginal (Level 1 of 4) to Slight Risk Friday.

DISCUSSION

Issued at 1103 PM CDT Mon Sep 28 2026

An upper level trough over the Southwest will ingest deep tropical moisture from the Pacific early this week. As the trough moves further east, an accompanying cold front is forecast to push into Central Texas, before likely stalling mid-week. Locally, continued southeasterly low level flow will advect additional warm and humid air from the Gulf across Deep South Texas. In the short term, this will continue to support daily heat concerns with afternoon heat index values ranging from 105-115. Heat Advisories may be needed daily through Thursday.

As the trough continues moving eastward, increased forcing across eastern Texas, combined with PWATs ranging from 2-2.5 inches will likely result in widespread rainfall across Deep South Texas Thursday afternoon into the weekend. The heaviest rainfall is most likely to occur Thursday and Friday, with probabilistic models supporting 48 hour rainfall accumulations from 7 AM Thursday through 7 AM Saturday ranging from 0.5-3 inches across the Mid and Lower Rio Grande Valley and 2 to 4 inches further west. The Weather Prediction Center has all of Deep South Texas in a Slight Risk (Level 2 of 4) for Excessive Rainfall Thursday, and a Marginal Risk (Level 1 of 4) for Excessive Rainfall across the coastal counties, with another Slight Risk over inland counties Friday.

The bulk of the model guidance suggest that the stalled frontal boundary may resume its southeastward motion Friday, bringing the cold front through Deep South Texas Friday afternoon into Friday evening. Light northerly surface flow behind the front could support cooler temperatures over the weekend, with high temperatures in the mid 80s to low 90s and overnight lows in the low to mid 70s. Easterly to southeasterly mid level flow will likely continue through the weekend, resulting in an overrunning pattern that will support overcast skies with generally light rain.

AVIATION

(06Z TAFS) Issued at 1235 AM CDT Tue Sep 29 2026

Light southeast winds and mostly clear skies prevail across Deep South Texas early this morning. Light southeast winds overnight will increase to 10 to 15 kts with gusts around 20 kts later this morning into the afternoon. There is a low (10-20%) chance for isolated convection along the sea breeze today. Winds are forecast to decrease later this evening. VFR conditions are expected to continue for the next 24 hours.

MARINE

Issued at 1103 PM CDT Mon Sep 28 2026

Winds and seas along the Lower Texas Coast are forecast to begin increasing Tuesday with additional increases anticipated mid week as pressure gradients tighten ahead of an approaching cold front. This will likely lead to adverse conditions on the Gulf and Laguna Madre with hazardous conditions possible later in the week. Small Craft Should Exercise Caution headlines will likely be needed beginning Tuesday, and Small Craft Advisories may be needed Thursday and Friday.

The cold front is forecast to move through the area Friday evening, with light northeasterly winds behind the front supporting lower seas through the weekend.

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

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 96 82 97 83 / 30 10 0 10 HARLINGEN 100 78 101 79 / 20 10 0 0 MCALLEN 102 82 103 83 / 10 10 10 0 RIO GRANDE CITY 103 80 104 80 / 0 0 0 10 SOUTH PADRE ISLAND 90 83 90 84 / 30 10 10 10 BAYVIEW/PORT ISABEL 95 80 96 80 / 30 10 10 0

BRO WATCHES/WARNINGS/ADVISORIES

TX...None. GM...None.