textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 539 AM CST Wed Dec 17 2025

* Patchy to areas of fog possible late tonight into Wednesday morning.

* Rain chances increase tonight into Wednesday with locally heavy rainfall Wednesday morning into Wednesday afternoon.

* Temperatures cool slightly on Friday in the wake of a cold front, otherwise well above normal temperatures persist into Christmas week.

* Life threatening rip currents are expected along the lower Texas coast through Wednesday.

DISCUSSION

Issued at 1034 PM CST Tue Dec 16 2025

A shortwave trough swings across northeastern Mexico and into the Gulf into late week, increasing moisture and instability across Deep South Texas Wednesday. The subtropical ridge returns this weekend into early next week with drier air. At the surface, low pressure develops along the coast, increasing the chance of showers and thunderstorms late tonight into Wednesday afternoon. PWAT values top 1.7 to 1.9 inches tonight through Wednesday, with the 00z sounding at BRO showing 1.65 inches already. For mid December, this is already above the 90th percentile and nearing daily max values.

As the shortwave treks east, and instability increases, there is concern convective rainfall rates will top 2-3 inches per hour mid to late Wednesday morning and persist into the afternoon. Most CAMs keep the bulk of the activity just offshore, north toward the Coastal Bend, and south of the border, but locally heavy rainfall will be possible across the mid to lower valley and eastern ranchlands of Brooks and Kenedy counties. The ECMWF Extreme Forecast Index (EFI) and Shift of Tails (SOT) also highlight a precipitation anomaly from northeastern Mexico north across the coastal counties into the Coastal Bend, potentially mostly driven by the well above normal moisture for mid December. NBM surged POP in waves of 60 to 80 percent across the lower valley in between breaks of 30 to 50 percent into Wednesday night. Have leaned into the best chance of rain being around daybreak through early Wednesday afternoon, nudging it further offshore into Wednesday night.

Have trimmed high temps a bit, especially along the coast, Wednesday afternoon due to the increased cloud cover and rain chances. A cold front drops south late Thursday into early Friday with a northerly wind shift bringing a briefly cooler but comfortable day. Southerly winds and well above normal temperatures return this weekend into Christmas week. A moderate risk of rip currents continues Wednesday and may persist into the weekend with a long period swell across the western Gulf. Patchy fog may develop overnight with the increased moisture and return again Wednesday night into Thursday morning.

AVIATION

(12Z TAFS) Issued at 539 AM CST Wed Dec 17 2025

Most of the convection has moved offshore, with light rain lingering at HRL and BRO. HiRes guidance is in fairly good agreement with keeping any convection offshore through the afternoon. Though there is some disagreement between the models on isolated showers developing inland this evening, the bulk of the guidance keeps any activity north of the TAF sites.

MVFR to IFR ceilings will likely linger through the morning, becoming VFR this afternoon. Light winds and mostly clear skies tonight could support widespread fog development early Thursday morning, likely resulting in IFR or LIFR visibilities.

MARINE

Issued at 1034 PM CST Tue Dec 16 2025

There is an increasing chance of showers and thunderstorms into Wednesday afternoon, with elevated seas and reduced visibility near any heavier showers and thunderstorms. Marine conditions generally improve through the remainder of the forecast period with southerly onshore flow, aside from a brief northerly wind shift behind a front on Friday that elevates seas through the afternoon.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 73 64 83 63 / 90 20 0 0 HARLINGEN 74 60 83 57 / 80 20 0 0 MCALLEN 76 62 85 60 / 50 10 0 0 RIO GRANDE CITY 76 57 85 55 / 30 0 0 0 SOUTH PADRE ISLAND 71 64 77 63 / 90 30 0 0 BAYVIEW/PORT ISABEL 72 63 81 62 / 90 20 0 0

BRO WATCHES/WARNINGS/ADVISORIES

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