textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 554 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

(12Z TAFS) Issued at 554 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.