textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 510 AM CST Wed Dec 10 2025

-Rain free and pleasant temperatures and humidity through Thursday, with a warming trend Friday and Saturday

-More unsettled and uncertain weather arrives Sunday through Tuesday, with increasing rain chances

-Dangerous surf, rising and roughening seas, and water run-up onto the beaches will make for difficult beach and boating conditions along the Lower Texas coast Sunday afternoon through Tuesday

DISCUSSION

Issued at 1051 PM CST Tue Dec 9 2025

Rest of tonight through Saturday Night: Overall sensible weather will be fair and pleasant, as the southern tip of Texas sits on the southwest side of the rather deep eastern U.S. upper-level trough that eventually flattens out by Friday night. Weak short waves ride from the southern Rockies into central Texas into Saturday, with the main effects being a bit more clouds and humidity on low level southerly flow.

Within the fair and pleasant period are some nuances. Through Wednesday evening, not much to discuss other than some patchy ground fog across portions of the northern ranchlands early Wednesday, with temperatures later Wednesday rebounding back into the upper 70s to lower 80s under plenty of sunshine and passing high clouds. The first nuance arrives later Wednesday night and Thursday. The aforementioned eastern U.S. deep trough gets a slight boost on its southwest flank, which is sufficient to push a weak cold front through south Texas - and now likely with enough push from a "bubble" high moving into southeast Texas to push the boundary across the lower Rio Grande.

Model blends have caught on to this, and both minimum and maximum temperatures Thursday are forecast to be 2-4 degrees lower than earlier today. The NAM-12, as it is wont to do, is sharpest with the change, carrying drier and cooler air along with a period of overcast skies to the populated RGV from early Thursday through mid to late afternoon, on light but notable northerly flow. Without a true strong push of shallow cold air, this is likely overdone - but at least in the ballpark. Bottom line? Drier and cooler surface air (compared to Wednesday) is becoming more likely - even the latest NBM indicates a 9 to 25% probability of mid afternoon temperatures below 70. So, while the current forecast for Thursday is about 3-7 degrees lower than Wednesday, it could be up to 10 degrees cooler (i.e. upper 60s to lower 70s) where clouds are slowest to clear.

"Bubble" surface high pressure cells in fast-moving flow are fleeting, and this will be the case by Thursday night and Friday. Will need to keep an eye on potential fog (locally dense) late Thursday night into Friday morning under light south/southeast flow and recovering dewpoints and warmer overnight temperatures but otherwise partly cloudy skies with slightly more humidity, with southeast winds picking up a bit are expected by Friday afternoon. The return flow persists into Saturday, with temperatures warming further and likely reaching 10 degrees above average (mid to upper 60s at Sunrise, mid to upper 80s by afternoon) for a temperature "bookend" to a week that began with near-record highs this past Sunday. Another warm (for mid December) night follows on Saturday night, with no rain expected on land.

Sunday through Tuesday: Changes arrive Sunday and continue through Tuesday. While the changes aren't earth-shattering, especially inland, the sensible weather is more unsettled. The main culprit is a reinforcing but short-wavelength shot of arctic-sourced air diving into the northeast U.S. Sunday into Monday. Behind the descending "piece" of the circumpolar vortex into the northeast is a strong and sprawling surface ridge of at least 1042 mb that eases across the Ohio Valley and into the mid Atlantic states late Sunday into Monday night. The base of the ridge dives into the northern Gulf states, and the remainder "bridges" across most of the Gulf by early Monday. This will bring a prolonged, long-fetch east-northeast flow across the Gulf, veering southeast above the surface as it reaches the foothills of the Sierra Madre. Despite a short-wave upper ridge moving overtop of the Valley, the upslope component with decent Gulf moisture will increase rain chances and potential QPF over an inch across the Rio Grande Plains/upper Valley Sunday afternoon/night into Monday, with the same moisture potentially shunting east Monday night and Tuesday as the upper ridge breaks down.

The current blends back away from rain chances Monday and Tuesday, but expect this to change a bit due to uncertainty in the pattern evolution with model handling of shortwave energy following the upper ridge. Regardless of the more unsettled weather, rain amounts look to be more beneficial, where they occur, as there is no deep tropical connection to the lower level upslope forcing - and uncertainty is greatest thereafter on location of heavier rain in Texas, which may shift from the Rio Grande Plains/upper Valley into the Edwards Plateau and central Texas. The broader east/northeast flow will nudge temperatures down especially by day, but only to or even just above average (mid 70s is average by then) for Monday and Tuesday.

AVIATION

(12Z TAFS) Issued at 510 AM CST Wed Dec 10 2025

Generally VFR conditions are expected to persist through the TAF cycle at all TAF sites. There is the potential for some early morning fog for the next couple of hours, but that should burn off quickly once the sun rises. Light winds are expected for the period as well.

MARINE

Issued at 1051 PM CST Tue Dec 9 2025

Now througth Saturday Night: Generally favorable boating conditions will be the story, with slight to moderate seas and generally light winds through the period. The one minor fly in the ointment is late Wednesday night into early Thursday, when a brief period of north flow up to 15 knots and seas possibly nudging to 4 feet occur behind the weak cold front. Outside of this period, generally south/southeast winds should remain at 10 knots or less, with little more than isolated streamer showers mainly east of 20 nm out.

Sunday through Sunday Night: East/east-northeast winds will increase behind the sprawling "bridging" surface ridge beginning as early as Sunday morning and picking up Sunday afternoon and especially Sunday night. Current forecast caps seas at 4 to 5 feet, but a reasonable high-end scenario would push values up to 7 feet or higher sometime Sunday night...and winds could edge over 20 knots at times - all requiring a Small Craft Advisory should this pan out.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 82 60 79 64 / 0 0 0 0 HARLINGEN 83 55 78 59 / 0 0 0 0 MCALLEN 84 57 78 62 / 0 0 0 0 RIO GRANDE CITY 83 52 75 56 / 0 0 0 0 SOUTH PADRE ISLAND 75 65 73 68 / 0 0 0 0 BAYVIEW/PORT ISABEL 80 60 77 62 / 0 0 0 0

BRO WATCHES/WARNINGS/ADVISORIES

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