textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 558 AM CDT Sun Sep 27 2026

- Hotter than normal temperatures will continue through Wednesday of next week.

- Widespread moderate (Level 2 out of 4) to major (Level 3 out of 4) heat risk with pockets of Extreme (Level 4 of 4) Heat Risk to continue across the region through Wednesday of next week.

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

- A welcome weather pattern change to cooler and wetter could take shape at the start of October (sometime mid next week into next weekend).

- Our next best and more widespread chances for rain (due to increased moisture, a cool front, and nearby shortwave trough) will come mid next week to the following weekend; currently have low-medium chances (30-60%) areawide in the Wednesday night through Sunday timeframe.

- The Weather Prediction Center (WPC) has all of Deep South Texas under a Marginal (Level 1 of 4) Risk for Excessive Rainfall for Wednesday (Day 5).

DISCUSSION

Issued at 950 PM CDT Sat Sep 26 2026

The heat will continue to be the main weather storyline through Wednesday of next week. However, by the Wednesday through Friday of next week timeframe (or as we move into the month of October), the storyline will shift towards the increasing chances for a major weather pattern change towards cooler and wetter conditions, driven by El Nino influences.

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

Saturday through Monday of next week, the strong heat dome that's been in place across Deep South Texas and the Rio Grande Valley will begin weakening. Despite the weakening of the ridge, it's influence overhead will be strong enough to continue yielding rain-free and hotter than normal temperatures. High temperatures during this time will range between the upper 90s to lower 100s.

Tuesday through Wednesday of next week is when things get interesting regarding our aforementioned pattern shift. Hurricane Polo during this time is expected to make landfall over the Baja Peninsula of California, northern Mexico, and eventually northern Texas. 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.

The combination of deep tropical moisture streaming in from these two source regions along with the aforementioned heat dome in place (though weakening) will result in a heat spike with high heat indices Tuesday and Wednesday. Increased humidity levels with dewpoints in the mid to upper 70s will result in a return to dangerous peak heat indices ranging between 105-113F degrees Tuesday and Wednesday. This will trigger widespread Major (Level 3 of 4) to Extreme Level 4 of 4) Heat Risk over the region. Special Weather Statements (SPSs) and/or a Heat Advisory may be needed Tuesday and Wednesday.

During this time (Tuesday through Wednesday of next week), a southeastward advancing cool front is expected to track across Texas gradually approaching Deep South Texas before possibly stalling 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 beginning Wednesday and persisting through the next weekend and possibly beyond.

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. Currently, we've have low-medium (30-60%) PoPs Wednesday night through Sunday areawide. It's too early to get into the exact impacts, but heavy rainfall is possible given the surge of tropical moisture. The Weather Prediction Center (WPC) has outlooked our entire area under a Marginal (Level 1 of 4) Risk for Excessive Rainfall on Wednesday (Day 5).

AVIATION

(12Z TAFS) Issued at 558 AM CDT Sun Sep 27 2026

Light to moderate winds and clear to partly cloudy skies will produce VFR conditions at the aerodromes through the next 24 hours.

MARINE

Issued at 950 PM CDT Sat Sep 26 2026

Generally, favorable marine conditions will persist through Monday of next week 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 the threat for showers and thunderstorms as well as increased seas. SCEC to Small Craft Advisories may be needed in the Tuesday night through Friday timeframe.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 97 78 96 80 / 10 0 20 10 HARLINGEN 100 74 99 75 / 0 0 10 0 MCALLEN 102 78 102 79 / 0 0 10 0 RIO GRANDE CITY 103 77 103 77 / 0 0 0 0 SOUTH PADRE ISLAND 89 82 89 82 / 0 10 10 10 BAYVIEW/PORT ISABEL 94 77 94 78 / 0 10 10 10

BRO WATCHES/WARNINGS/ADVISORIES

None.