textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1039 PM CDT Wed Jul 22 2026

- Daily above average temperatures persist, maximizing around 100 to 107+ F, with heat indices of 105 to 111+ F, continuing moderate to major heat risks (levels 2/4 and 3/4), possibly becoming mostly major with pockets of extreme heat risks (level 4/4) by the middle of next week.

- A Heat Advisory is in effect for Zapata and Starr counties from 1 PM to 7 PM Thursday for heat indices of 111 to 113 F and a SPS is in effect for Jim Hogg, Brooks and inland Kenedy counties for heat indices of 108 to 111 F, generally within the hours of 12 PM to 7 PM.

- The Weather Prediction Center (WPC) highlights most of deep south Texas within a Marginal (level 1 of 4) risk of possible (at least 5% chance) isolated flash flooding from excessive and heavy rainfall to as far south as northern/northwestern Cameron and southeastern Hidalgo counties for Thursday through Thursday night.

- Chances of rain increase throughout Thursday to as much as a medium to likely (50-80%) chance by Thursday evening/night and total rainfall amounts of 1.0-2.0+ inches are possible across the Northern Ranchlands and Rio Grand Plains.

- A low risk of life-threatening rip currents continues through Thursday afternoon, but stay tuned for updates on the potential for increased risks of rip currents, elevated surf and minor coastal flooding possible later this week in association with Tropical Storm Bertha.

DISCUSSION

Issued at 1039 PM CDT Wed Jul 22 2026

We will start off the discussion with the most immediate focus of the forecast, which is the anticipated rainfall associated with Tropical Storm Bertha, projected to remain more or less on a westward track, bringing the main and most direct impacts to coastal/southern Louisiana and the Upper Texas coast/southeastern Texas through the end of the work-week. Meanwhile, northeasterly upper level winds circulating the southeastern side of a 549-497+ dam high pressure aloft is anticipated to advect associated deep, tropical moisture and convection southwestward to southern and deep south Texas through the next 24-48 hours. Ahead of the unsettled weather, we anticipate strong subsidence aloft to result in another day of nearly widespread low/mid 100s along/west of I-69 E with upper 100s (107+ F) over the Rio Grande Plains along with a mostly major heat risk as dewpoints rise. A Heat Advisory is in effect for Zapata and Starr counties from 1 PM to 7 PM Thursday for heat indices of 111 to 113 F and a SPS is in effect for Jim Hogg, Brooks and inland Kenedy counties for heat indices of 108 to 111 F, generally within the hours of 12 PM to 7 PM. Depending on when clouds increase, temperatures could fall beneath advisory and statement criteria before 7 PM.

At this time, there still remains considerable amount of uncertainty on the timing and southward extent of the moisture field, the level to which moisture content increases and the resulting coverage, rainfall rates and total rainfall amounts of the arriving convection. At this time, we generally expect for low to medium (20-40%) chances of rain during the morning and afternoon to spread westward from the coast and increase to as much as a medium to likely (50-80%) chance along/west of US-281 Thursday evening into late Thursday night. Meanwhile, chances of of rain begin diminishing from west to east, beginning at the coast by late Thursday night before all rain exits the CWA by possibly Friday morning. In general, the highest chances of rain and rainfall amounts are likely to be across the Rio Grande Plains and the Northern Ranchlands along/west of US-281, where 1.0 to 2.0+ inches of rain are possible. The latest probabilistic NBM guidance supports around a 30-40% chance of rainfall amounts exceeding 2.0 inches. Due to the potential, though low confidence, for very high moisture content (PWATs exceeding 2.6+ in.), more widespread heavy rain and/or a southward shift, WPC highlights most of the region (as far south as northern/northwestern Cameron County and southeastern Hidalgo County) within a Marginal risk (at least 5% chance) of possible isolated flash flooding from excessive and heavy rainfall Thursday through Thursday night.

Additionally, although SPC indicates a general chance of sub-severe thunderstorms, a decent amount of instability (CAPE near 1,000 J/Kg or more) and possibly 25-30+ knot shear could be enough to generate a few strong thunderstorms capable of producing heavy rain and wind gusts up to 40 mph. Chances of severe thunderstorms are low but not completely out of the question.

Otherwise, high pressure aloft, briefly mentioned above, retreats to and builds over the Desert Southwest through this weekend, possibly peaking as much as 600 dam on Saturday before gradually shifting back to the Southern Plains by the early to middle parts of next week, generally maintaining 594-497 dam. A more distant high over the weekend should help slightly cool high temperatures by a few degrees, but then widespread inland highs in the low/mid 100s return by Monday as the high pressure advances eastward again. Mostly moderate heat risks, with pockets of major along/east I-69 E, are anticipated Friday through Sunday, but major heat risks begin to expand next Monday, becoming mostly major with pockets of extreme heat risks by the middle of next week as pulses of moisture coincide with increasing subsidence aloft. Additional SPSs are likely as daily afternoon heat indices peak around 105 to 111+ F, especially across the inland and coastal portions of Cameron, Willacy and Kenedy counties. Heat Advisories are also possible by early next week.

A low risk of life-threatening rip currents continues through Thursday afternoon. As the week progresses, potential long period swell and perhaps elevated surf, generated by Tropical Storm Bertha, could arrive to the Lower Texas coastal waters later in the week; elevated risks of life-threatening rip currents, higher surf and minor coastal flooding are possible and may lead to more dangerous beach and swimming conditions.

AVIATION

(00Z TAFS) Issued at 615 PM CDT Wed Jul 22 2026

Southeasterly winds continue at all terminals at this time, ranging from around 7 knots at KMFE and around 10-15 knots, with gusts to 20 knots at KBRO and KHRL. Southeasterly winds are likely to become gentle or light and variable following sunset this evening. Conditions should remain VFR, though there is a low probability (less than 30%) chance of rain tomorrow morning, slightly increasing into the afternoon hours which could briefly reduce ceilings and visibility. Thunderstorms are possible as well. However, confidence still remains low to medium at this time and there is the potential for chances of rain to increase and shift to an earlier start time, perhaps by late morning or early afternoon, as opposed to later in the evening, beyond the 00Z TAF timeframe. Rain could be heavy at times as well.

MARINE

Issued at 1039 PM CDT Wed Jul 22 2026

Gentle to moderate southeasterly winds, occasionally fresh, with slight to moderate (2-4 ft) seas are expected to enhance to mostly moderate to fresh, strong at times, with moderate (3-5 ft) seas by late Thursday afternoon, continuing through Friday night, during which time Small Craft Exercise Caution conditions are likely. Although the most direct impacts from Tropical Storm Bertha, moving west over the northern Gulf, are currently anticipated to remain well to the north, slightly elevated seas from associated swell could arrive to the Lower Texas coastal waters later this week and/or this weekend. Otherwise, gentle to moderate southeasterly winds and slight to moderate (2-5 ft) seas resume on Saturday.

Chances of rain increase tonight to as much as a medium to likely (50-80%) chance by Thursday morning, wane a bit into the late afternoon hours before increasing back to a medium to likely (40- 70%) chance by the evening hours. Chances gradually diminish from east to west to 10% or less by late Thursday night.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 80 96 81 96 / 0 30 20 0 HARLINGEN 77 99 78 98 / 0 40 40 0 MCALLEN 80 104 81 101 / 0 20 60 10 RIO GRANDE CITY 80 105 79 101 / 0 30 70 10 SOUTH PADRE ISLAND 80 88 81 88 / 0 40 20 0 BAYVIEW/PORT ISABEL 79 95 79 94 / 0 40 30 0

BRO WATCHES/WARNINGS/ADVISORIES

TX...Heat Advisory from 1 PM to 7 PM CDT Thursday for TXZ248-252.

GM...None.