textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 554 AM CDT Fri Sep 25 2026

- Low to medium (10-40%) rain chances along the sea breeze on Friday across Deep South Texas.

- Above average temperatures (around 5-10 degrees above normal) to 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.

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

- Our next best and more widespread chances for rain (due to a cool front and nearby shortwave trough) will come mid to late next week; currently have low-medium chances (30-40%) areawide in the Wednesday through Friday timeframe.

DISCUSSION

Issued at 1113 PM CDT Thu Sep 24 2026

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

We start off the forecast period tonight where most of the diurnally and sea breeze driven rain showers continue to wane across the region. Can't rule out an isolated shower or two is spots tonight. The region continues to sit on the southern periphery of a strong and broad 591-594 dam sub-tropical heat dome. This setup is helping drive a persistent easterly flow regime over the region which is helping to drive the day-to-day sea breeze convection. Friday will present another day and opportunity of isolated (hit- or-miss variety) sea breeze showers over the region, primarily during the afternoon into the early evening hours. Chances for precipitation is low-medium (10-40%) for Friday.

Saturday through Monday of next week, the aforementioned heat dome will strengthen and expand over the region. Due to the greater influences of the strengthening/expanding heat dome, rain chances will be suppressed Saturday through Monday due to increased subsidence. That said, Saturday through Monday will continue to feature hotter than normal temperatures and mostly dry conditions.

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 and move into northern Mexico. 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) could 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 will be traversing across Texas gradually approaching Deep South Texas. Furthermore, 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 shortwave trough, an approaching cool front, and the influx of deep tropical moisture from the Gulf of America and the Eastern Equatorial Pacific Ocean will support widespread chances for showers and thunderstorms beginning Wednesday and persisting through then end of next week and possibly longer. This is the potential pattern shift that we're 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 maintained low-medium (30-40%) PoPs Wednesday through Friday areawide. It's too early to get into the exact impacts, but heavy rainfall is possible given the surge of tropical moisture.

AVIATION

(12Z TAFS) Issued at 554 AM CDT Fri Sep 25 2026

VFR will prevail at the aerodromes through the next 24 hours, with light to moderate winds and clear to partly cloudy skies. A TEMPO for convection remains added to the TAFs, with timing based on the HRRR model.

MARINE

Issued at 1113 PM CDT Thu Sep 24 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/Wednesday and points forward, conditions will become more adverse due to the threat for showers and thunderstorms as well as SCEC conditions developing.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 95 80 95 79 / 40 10 10 0 HARLINGEN 98 76 99 74 / 30 0 10 0 MCALLEN 98 79 99 78 / 40 0 20 0 RIO GRANDE CITY 99 77 101 77 / 30 10 0 0 SOUTH PADRE ISLAND 90 83 89 82 / 20 0 10 0 BAYVIEW/PORT ISABEL 94 79 94 78 / 20 0 10 0

BRO WATCHES/WARNINGS/ADVISORIES

None.