textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1247 PM 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.

- Cooler and wetter conditions are expected late this week into early next week due to a frontal passage and a multi-day rainfall event Thursday through 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 flooding rainfall for Thursday, a Marginal (level 1 of 4) to Slight Risk on Friday, and a Marginal Risk along the coast on Saturday.

DISCUSSION

Issued at 1247 PM CDT Wed Sep 30 2026

There remains a Major to Extreme risk of heat-related illness today and Thursday afternoon. A Special Weather Statement is in effect and Heat Advisories may be needed.

An upper level trough, slow-moving surface frontal boundary, and deep tropical moisture continues to work east into this weekend and combine with humid southeasterly flow off the Gulf to bring a much-needed chance of beneficial rainfall into next week. The best chance of persistent heavy rainfall Thursday into Saturday remains across Zapata, Jim Hogg, Starr, Brooks, and northern Hidalgo counties, generally nudging eastward through the Rio Grande Valley and lower Texas coast with the frontal passage through late this weekend.

Areas of advanced drought conditions may experience excessive runoff where any heavy rain persists. There is some concern for flash flooding where heavier rain and excessive runoff occurs Thursday into Saturday, especially across the brush country, where flash flooding is more common. The Weather Prediction Center has continued a Moderate Risk (at least 40 percent chance) of flooding rainfall across Zapata, Jim Hogg, and 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 the Rio Grande Valley. The chance of flooding rainfall continues Friday into Saturday across all of Deep South Texas and along the coast Saturday into Monday.

Rainfall amounts of generally 2 to 4 inches are expected across Deep South Texas and the Rio Grande Valley into Saturday, with an additional 1 to 3 inches of rainfall expected into Monday, and locally higher amounts where any heavier rainfall persists. 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 into Saturday morning, with an additional 2 to 3 inches by Monday morning, mainly along and east of US281/I69C. Have held off on any Flood Watches at this time but will continue to monitor through the shift.

Expect a breezy afternoon continuing overnight into Thursday as the pressure gradient strengthens and a LLJ sets up overnight. 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 1247 PM CDT Wed Sep 30 2026

VFR conditions are expected to generally prevail through the TAF period with breezy southeasterly winds this afternoon into Thursday. There is a low chance of an isolated shower or thunderstorm over the next couple of hours and a higher chance of showers and thunderstorms Thursday afternoon, just beyond this TAF period.

MARINE

Issued at 1247 PM CDT Wed Sep 30 2026

The pressure gradient tightens along the lower Texas coast into Thursday as an upper level low and slow-moving frontal boundary work through Texas and approach coastal waters. Expected seas to build 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 1247 PM CDT Wed Sep 30 2026

There is an increased threat of heavy rainfall along the Rio Grande into this weekend which will 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. 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. Areas that have been dry for months may become inundated by the weekend or early next week with flowing water.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 83 97 81 95 / 20 30 50 70 HARLINGEN 80 100 76 97 / 20 50 50 80 MCALLEN 83 102 80 97 / 20 50 70 80 RIO GRANDE CITY 81 102 77 93 / 30 70 90 90 SOUTH PADRE ISLAND 84 90 83 89 / 20 20 40 40 BAYVIEW/PORT ISABEL 81 96 79 93 / 20 30 40 60

BRO WATCHES/WARNINGS/ADVISORIES

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