textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1216 PM CDT Tue Sep 29 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 all of 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 1216 PM CDT Tue Sep 29 2026

Well-above normal heat and a Major to Extreme risk of heat- related illness continues through Wednesday. A Heat Advisory may be needed both Wednesday and Thursday.

An upper level trough, slow-moving frontal boundary, and deep tropical moisture arrive from the west by late week and combine with humid southeasterly flow off the Gulf, and at least initial instability on Thursday, to bring a much-needed chance of mostly beneficial rainfall... and a low to medium chance of flash flooding... Thursday into next week. The best chance of persistent heavy rainfall Thursday into Saturday remains across Zapata, Jim Hogg, Starr, and Brooks counties, with areas of advanced drought conditions likely seeing excessive runoff where heavy rain persists.

The Weather Prediction Center has posted a Moderate Risk (at least 40 percent chance) of flooding rainfall across Zapata, Jim Hogg, western Brooks, and most of Starr counties Thursday through Thursday night, with a Slight Risk (at least 15-25 percent chance) of flooding rainfall across the remainder of Deep South Texas, including most of the Rio Grande Valley. The chance of flooding rainfall continues Friday and Saturday across all of Deep South Texas. The Storm Prediction Center has posted a Marginal Risk (level 1 of 5) of Severe Weather for portions of Zapata County Thursday into Thursday night.

Rainfall amounts of generally 2 to 4 inches are expected across Deep South Texas and the Rio Grande Valley Thursday into Saturday, with higher amounts where any heavier rainfall persists and additional rounds of rainfall expected through the weekend. The latest 48-HR probabilistic guidance indicates there is a low (10 percent) chance of up to 4 to 6 inches across areas generally west of US281/I69C by Saturday morning, with an additional 1 to 3 inches by Monday morning. A Flood Watch may be needed Thursday into the weekend.

Expect a breezy Wednesday into Thursday as the pressure gradient strengthens. The increased chance of rain and cloud cover, as well as a northerly wind shift by the weekend into early next week, will bring a taste of Fall and welcomed break to the heat, with below normal temperatures Saturday into early next week. Will continue to monitor beach and marine hazards over the weekend, with a potential for tidal run-up and elevated risk of life- threatening rip currents.

AVIATION

(18Z TAFS) Issued at 1216 PM CDT Tue Sep 29 2026

VFR conditions are expected to prevail through the TAF period with a southeast breeze through the afternoon. There remains a low chance of a shower or a thunderstorm into early afternoon, with brief MVFR ceilings.

MARINE

Issued at 1216 PM CDT Tue Sep 29 2026

The pressure gradient tightens along the lower Texas coast mid- week as an upper level low and slow-moving frontal boundary work through Texas and approach coastal waters. Expected seas to build Wednesday into Thursday with SCEC to borderline SCA conditions. Light to moderate northerly winds are expected behind the frontal boundary Saturday into early next week with Fall-like conditions, including light rain or drizzle and decreased visibility, especially near the coast.

HYDROLOGY

Issued at 1216 PM CDT Tue Sep 29 2026

There is an increased threat of heavy rainfall across portions of Texas along the Rio Grande late this week into this weekend which will likely lead to a rise in water levels along the Rio Grande, Main Floodway, North Floodway, and Arroyo Colorado into next week. The Falcon Reservoir remains very low and has plenty of room to hold any increased flow along the Rio Grande upstream of Falcon. For any interests stationed or positioned within levees downstream of Falcon, including along the floodways and Arroyo Colorado, through Starr, Hidalgo, and Cameron counties, please continue to monitor river forecasts and water levels into next week or plan to re-position or station any assets outside of any levees.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 82 97 82 97 / 20 0 20 30 HARLINGEN 78 101 80 100 / 10 10 10 40 MCALLEN 82 103 83 102 / 10 0 10 50 RIO GRANDE CITY 80 104 81 102 / 0 0 10 60 SOUTH PADRE ISLAND 83 90 83 90 / 10 10 30 20 BAYVIEW/PORT ISABEL 80 96 80 96 / 10 0 20 30

BRO WATCHES/WARNINGS/ADVISORIES

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