textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 630 AM CDT Mon Sep 28 2026

- Hotter than normal temperatures will continue through Thursday.

- 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.

- Heat spikes are possible Tuesday-Thursday with dangerous heat indices ranging between 105-115F degrees; Special Weather Statements (SPSs) and Heat Advisories may be needed.

- Confidence is increasing on a significant weather pattern change towards markedly cooler and wetter conditions later this week; this includes a multi-day heavy rain and flash flood potential Thursday through early next week.

- Preliminary rainfall amounts of 2-4 inches with locally higher amounts is possible Thursday through next Sunday night.

- The Weather Prediction Center (WPC) has all of Deep South Texas under a Slight (Level 2 of 4) Risk for Excessive Rainfall for Thursday (Day 5).

- Breezy southeast winds 15-25 mph with gusts up to 35 mph or so will result in SCEC to Small Craft Advisories for the Laguna Madre and the Gulf Tuesday and Wednesday as well as increased rip current risks along the beaches.

DISCUSSION

Issued at 1113 PM CDT Sun Sep 27 2026

The two main weather storylines for the week ahead is 1) the heat through Thursday, and 2) the increasing chances for a significant weather pattern shift, featuring wetter and cooler changes, courtesy of the influences of a strong El Nino later this week.

We start off the forecast period tonight where dry, warm, and humid conditions will persist under partly cloudy to mostly cloudy skies.

THE HEAT STORYLINE

The strong heat dome that's plagued Deep South Texas and the Rio Grande Valley over the past week is currently weakening. Despite the weakening of the heat dome, it's influence overhead will be strong enough to continue yielding mainly rain-free and hotter than normal temperatures through Wednesday night. During this time, high temperatures will range between the upper 90s to lower 100s. A heat spike is possible Tuesday through Thursday, ahead of the coming pattern change. Deep tropical moisture from the Gulf and the eastern equatorial Pacific will stream into the region, Tuesday through Thursday. Though the aforementioned heat dome will be weakening, it will be strong enough for hot temperatures to persist. These hot temperatures combined with an influx or surge of moisture will result in dangerously hot heat indices Tuesday through Thursday.

Forecasted peak heat indices during this time is expected to range between 105-115F degrees. This will trigger widespread Major (Level 3 of 4) with pockets of Extreme (Level 4 of 4 ) Heat Risk during this timeframe. Special Weather Statements and Heat Advisories may be needed to account for the surge in dangerously hot heat indices. Very warm overnight low temperatures in the upper 70s to lower 80s will provide little to no relief.

It's also worth noting that Tuesday and Wednesday will be quite breezy. An approaching cool front from northwestern Texas and a large Bermuda High to the east will result in an enhanced pressure gradient ahead of the pattern change that's to come. This will result in breezy southeasterly winds 15-25 mph gusting as high as 35 mph or so Tuesday and Wednesday. These winds could trigger Small Craft Exercise Caution (SCEC) and Small Craft Advisories along the Laguna Madre and parts of the Gulf (see MARINE SECTION). These winds will help in aiding moist and warm air advection (WAA) during this time.

THE MAJOR WEATHER PATTERN CHANGE STORYLINE

As touched on in the previous section, confidence continues to increase on a significant weather pattern featuring markedly wetter and cooler conditions, after such a brutally hot and dry few months. Forecast models/ensembles continue to show Hurricane Polo making landfall over the Baja Peninsula of California before tracking over northern Mexico and eventually northern Texas Monday through Wednesday of this week. Along with the re-curvature of Hurricane Polo, deep tropical moisture from the Eastern Pacific will stream will begin to stream into the region from the west-southwest. Meanwhile, deep tropical moisture from the Gulf of America will begin to stream into the region from the south, courtesy of a large Bermuda high to the east.

Meanwhile, during this same time, a southeastward advancing cool front is expected to track across Texas gradually approaching Deep South Texas before possibly stalling just to our north. Meanwhile, there are indications of a weak shortwave trough and mid-upper energies residing near Deep South Texas and northeast Mexico. The combination of a nearby mid-upper impulses, a nearby stalled/stalling cool front, and the influx of deep tropical moisture from both the Gulf of America and the Eastern Equatorial Pacific Ocean will support widespread chances for showers and thunderstorms later this week.

Over the past 24-48 hours, the timing has scaled back some. So instead of the rain beginning on Wednesday, the rains are expected to arrive Thursday afternoon/evening. These rains are expected to persist through next weekend and possibly beyond. These breakthrough rains will effectively put a dent to the D2 (Severe) to D4 (Exceptional) Drought over the region. This has the makings of a multi-day heavy rainfall and flash flooding event. Run-off and flash flooding is certainly possible due to 1) how hard and impervious the soils are, 2) how efficient the rainfall will be given the moisture laden environment, and 3) the likelihood that showers and thunderstorms will track over many of the same areas and could be slow-movers (atmospheric river-like). Now is the time to begin preparing for this multi-day heavy rain and potential flash flooding event. That includes checking your tires, brakes, wipers, clearing sewers, drainages, etc. See weather.gov/safety/flood for more tips on flood safety.

That said, we have medium-high or categorical PoPs ranging between 40-80% for most of the time period from Thursday into Monday of the following week (Oct 1-5, 2026). Preliminary rainfall amounts between Wednesday night and Sunday night range between 2-4 inches with locally higher amounts. Finally, the Weather Prediction Center (WPC) has all of Deep South Texas and the Rio Grande Valley under a Slight Risk (Level 2 of 4) for Excessive Rainfall for Thursday.

This is the potential pattern shift that we've been closely monitoring, and if realized, will bring the breakthrough rains that we've been waiting for so long as well as a notably cooler pattern due to the increase cloud coverage and rains. This potential pattern shift to start October has El Nino written all over it. Again, we will continue to closely monitor forecast trends in the days ahead and fine tune the forecast as needed.

AVIATION

(12Z TAFS) Issued at 630 AM CDT Mon Sep 28 2026

Light and variable winds prevail across Deep South Texas early this morning. Light east winds this morning will become east to southeast around 10 knots later this morning into the afternoon. Some wind gusts around 20 knots will be possible in the afternoon. Winds are expected to decrease later this evening. VFR conditions will continue for the next 24 hours.

MARINE

Issued at 1113 PM CDT Sun Sep 27 2026

Generally, favorable marine conditions will persist through Monday with low to moderate seas (wave heights between 1-3 feet) and winds. Tuesday night and points forward, conditions will become more adverse due to increased winds Tuesday and Wednesday, the threat for showers and thunderstorms, and increasing seas. SCEC to Small Craft Advisories may be needed in the Tuesday night through Saturday timeframe.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 96 80 96 82 / 10 10 20 10 HARLINGEN 99 77 100 78 / 10 10 30 10 MCALLEN 102 80 102 82 / 0 10 10 0 RIO GRANDE CITY 102 78 103 80 / 0 0 0 0 SOUTH PADRE ISLAND 89 82 89 84 / 10 20 20 10 BAYVIEW/PORT ISABEL 94 78 94 80 / 10 10 30 10

BRO WATCHES/WARNINGS/ADVISORIES

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