114 FXUS64 KBRO 240326 AFDBROArea Forecast Discussion National Weather Service Brownsville TX 1026 PM CDT Tue Sep 23 2025
...New DISCUSSION, MARINE...
.KEY MESSAGES... Updated at 1024 PM CDT Tue Sep 23 2025
* Hot and humid with isolated chances for showers and thunderstorms again on Wednesday; Major (Level 3 of 4) Heat Risk expected with heat indices between 105-113F.
* Strong to severe thunderstorms are possible Wednesday night into Thursday; heavy rainfall, lightning, and strong winds will be the primary threats.
* There is a Marginal (Level 1 of 5) Risk for severe thunderstorms across the Northern Ranchlands Wednesday night into Thursday.
* There is a Marginal (Level 1 of 4) Risk for Excessive Rainfall across Brooks, Jim Hogg, and Zapata Counties Wednesday night into Thursday.
* Low grade (20-30%) chances for showers and thunderstorms will continue for much of the forecast period from Friday to Wednesday of next week with cooler/near normal temperatures.
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.DISCUSSION... Issued at 1024 PM CDT Tue Sep 23 2025
The main weather headline during the forecast period will focus on the potential for strong to severe thunderstorms along with locally heavy rainfall in the Wednesday night through Thursday timeframe as a cold front advancing southward across the state of Texas approaches the region. Afterwards, an unsettled or somewhat unsettled weather pattern remains on the table with day-to-day or near day-to-day chances for showers and thunderstorms.
We start off the forecast period on Wednesday, that will feature another warmer than normal, humid day with mainly rain-free conditons. While most will experience rain-free conditions, there is an isolated to widely scattered chance (20-30%) for showers and thunderstorms to develop amid increased diurnal heating, elevated precipitable water (PWAT) values, and some sea breeze interactions. Wednesday is also progged to be our warmest day of the forecast period with readings topping out in the mid 90s near the Lower Texas Coast to the lower 100s west of IH-69C. Peak heat indices are expected to range between 105-113F degrees, which will result in Major (Level 3 of 4) Heat Risk.
Wednesday-Wednesday night, a line of strong to severe thunderstorms driven by increased positive vorticity advection (PVA) and sfc convergence in addition to an unstable airmass will be taking place across central Texas. Hi-res CAM guidances are suggesting this activity shifting southward in conjunction with the aforementioned southward advancing cold front. There still remains uncertainties in how far south the cold front will reach, but forward momentum from the line of showers and storms to our north could reach into Deep South Texas in the Wednesday night to Thursday timeframe. PoPs are expected to increase from low to medium (20-40%) chances Wednesday night (highest across the Northern Ranchlands) to categorical (55- 70%) chances on Thursday.
Should these storms continue southward into Deep South Texas, Sfc- Based CAPE (SBCAPE) values between 1,000-2,000 J/kg and Downdraft CAPE (DCAPE) values between 500-1,500 J/kg will support the threat for strong to severe thunderstorms capable of producing damaging winds. The Storm Prediction Center (SPC) has an isolated or Marginal (Level 1 of 5) Risk for severe thunderstorms for the Northern Ranchlands on Wednesday night in its SWODY 2, with damaging winds being the primary threat.
Additionally, the Weather Prediction Center (WPC) has a Marginal (Level 1 of 4) Risk for Excessive rainfall for our northwestern sections that includes Brooks, Jim Hogg, and Zapata Counties in its Day 2 ERO for Wednesday night into Thursday. While heavy rainfall is expected with any storms, dry antecedent soils and high FFGs will limit the widespread threat for flooding across these areas.
With the cold front potentially stalling out over the region or just to the north, another round of showers and thunderstorms could take place Thursday afternoon/evening, coinciding with peak sfc heating. Categorical (80-90%) chances for PoPs remain in place through the day on Thursday.
Rain chances begin to decrease on Friday as the aforementioned cold front either washes out or shifts south into northeastern Mexico. Rain-free conditions are expected to persist through Saturday night with high pressure in control over the region and to our north. Sunday through Wednesday, there are low grade chances (20-30%) for isolated to widely scattered showers and thunderstorms areawide. Temperatures Thursday through Wednesday of next week will average out closer to normal levels with highs in the lower 90s and lows in the upper 60s to mid 70s.
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.AVIATION... (00Z TAFS) Issued at 609 PM CDT Tue Sep 23 2025
VFR conditions are expected to prevail through the 00z TAF cycle. There could be a few MVFR clouds around from time to time.
Southeast winds will range between 5-15 kts through the forecast period. Winds could gusts up to 25 kts during the afternoon hours.
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.MARINE... Issued at 1024 PM CDT Tue Sep 23 2025
Outside of the chance for showers and thunderstorms, marine conditions will be favorable with low to moderate winds and seas through the forecast period.
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.PRELIMINARY POINT TEMPS/POPS... BROWNSVILLE 93 80 94 79 / 20 10 30 20 HARLINGEN 96 76 97 75 / 10 0 30 20 MCALLEN 100 80 100 80 / 0 0 20 20 RIO GRANDE CITY 101 77 102 76 / 0 0 20 30 SOUTH PADRE ISLAND 89 83 89 81 / 20 20 30 20 BAYVIEW/PORT ISABEL 92 79 93 78 / 20 10 30 20
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.BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. &&
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SHORT TERM...23-Evbuoma LONG TERM....23-Evbuoma AVIATION...23-Evbuoma
NWS BRO Office Area Forecast Discussion