textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1040 PM CDT Tue May 5 2026

Key Messages:

* Elevated relative humidity and a spike in temperatures result in a Major Heat Risk (Level 3 of 4) Wednesday afternoon as heat indices ("real feel" temperatures) soar to 105-110+ F across the region.

* A Heat Advisory is in effect from 1 PM to 7 PM Wednesday for Southern Hidalgo and inland portions of Cameron, Willacy and Kenedy counties, where indices are likely to exceed 111 F for several hours, potentially briefly reaching as high as 116 F. * A medium risk of rip currents continues through Wednesday afternoon.

* Cold front likely moves through Thursday afternoon or Thursday evening, increasing chances of rain from developing showers and thunderstorms to as much as a medium to likely (50-80%) chance Thursday night, followed by a low to medium (30-60%) chance on Friday.

* Uncertainty remains high and probabilities are low and conditional, but there is a gradually increasing signal for strong to severe thunderstorms late Thursday afternoon or evening, with hail and strong winds possible.

DISCUSSION

Issued at 1040 PM CDT Tue May 5 2026

Another day of brutal temperatures and heat indices is on tap for Deep South Texas on Wednesday as a trough moving into northern Mexico pushes a mid/upper level high pressure eastward into the central Gulf by Thursday, minimizing cloud cover while southeasterly flow, gusting to 20-30 mph further east, advects in higher moisture content. Additionally, a dryline moving into at least the western portions of our region in the afternoon brings in downslope compressional heating, further spiking temperatures to as high as the lower 100s along/west of US-281 and upper 90s elsewhere. Factoring in elevated relative humidity, a Major Heat Risk is expected as heat indices reach 105-110+ F across most of the CWA. A Heat Advisory is in effect from 1 PM to 7 PM Wednesday for Southern Hidalgo and inland portions of Cameron, Willacy and Kenedy counties, where indices greater than 111 F are expected to last for several hours, potentially briefly topping out at 116 F. This type of heat puts everyone at risk for heat-related illnesses, particularly for those without effective cooling or hydration. Thus, we recommend drinking plenty of water and avoiding strenuous activities during the afternoon and early evening hours. Drier air moving in behind the dryline should keep apparent temperatures a bit lower across the Rio Grande Plains, most of the Upper RGV as well as western portions of the Northern Ranchlands. However, a SPS may be issued overnight or Wednesday morning for these areas as well, where indices could still reach 111 F or higher for an hour or two.

The trough moves north of Deep South Texas Wednesday night into Thursday morning and a building surface high pressure over the Southern Plains pushes a cold front into Deep South Texas Thursday afternoon or Thursday evening. Overall, the latest expectations of the front is for it to slow its southward movement across the region while also developing showers and thunderstorms, gradually increasing chances of rain from north to south Thursday afternoon to as much as a medium to likely (50-80%) chance Thursday night. Increasing cloud coverage throughout Thursday should keep high temperatures in the 80s/90s, though 100-105 F heat indices across most of the RGV likely result in a Moderate Heat Risk (Level 2 of 4).

As discussed previously, although uncertainty remains high and probabilities remain low, there is a gradually strengthening signal for a conditional risk of strong to severe convection perhaps as early as late Thursday afternoon or Thursday evening, with convection beginning over the northwestern areas (Rio Grande Plains and the Northern Ranchlands) and moving southeastward into the evening or nighttime hours. At this time, the RAP and GFS are doing a decent job of initializing the latest upper air conditions and indicate a near-surface cap Thursday evening with MUCAPE of 1,000-2,000 J/kg and steep mid-level lapse rates supportive of at least 1" hail fruther west before trending downward overnight. The main difference is that the GFS, which can be viewed as the reasonable worst case scenario at this point, portrays a drier and more unstable airmass by the time convection initiates, with MUCAPE values exceeding 2,000 J/kg along/west of US-281, steeper low-level lapse rates and higher surface-based CAPE values, though capped. In the GFS solution, deep and strong convection developing to the northwest would pose a primary hail threat earlier in the event before transitioning a to strong to damaging wind threat as storms move southeastward and potentially break the cap.

On the flip side, some CAMs, such as the 18Z NAM 3km run, indicate the front sweeping quickly through the region Thursday morning, bringing stable air and cooler temperatures behind and little precipitation, if any at all, into Thursday night. Thus, the severe risk reamins conditional at this time. Regardless, the front is expected to have moved through at some point by Thursday evening or Thursday night. A low to medium (30-60%) chance of rain continues into Friday as a potential mid- level disturbance moves through ahead of a cut-off low aloft to the west. High temperatures rise from the 80s/90s on Friday back to widespread 90s on Saturday and Sunday, with a Moderate Heat Risk possible on Sunday. A weak cold front is possible Sunday night or Monday, which could bring a low chance of unsettled weather for the beginning of next week.

A medium risk of rip currents continues through Wednesday afternoon.

AVIATION

(00Z TAFS) Issued at 602 PM CDT Tue May 5 2026

Enhanced low level moisture from southeasterly flow has already led to MVFR ceilings (2,000 ft) at KBRO while remaining broken VFR (3,500 ft) at KHRL at this time. Breezy conditions (SE around 15 knots and gusting to 20 knots) continue overnight as MVFR ceilings spread across all terminals. There is the potential for IFR at KBRO from pre-dawn through sunrise, though have kept out of the TAFs as highest probabilities are further east and breezy southeast winds could keep ceilings slightly elevated. VFR skies return by midday or the afternoon and breezy south-southeasterly winds persist at KBRO and KHRL, while a dryline near KMFE will likely cause winds to drop off and turn to east-southeasterly in the afternoon.

MARINE

Issued at 1040 PM CDT Tue May 5 2026

The pressure gradient continues to loosen across the region, though Small Craft Exercise Caution headlines continue through tonight as moderate to fresh southeasterly winds and moderate (3-5 ft) seas gradually reduce to moderate on Wednesday and gentle to moderate Wednesday night with slight to moderate (2-4 ft) seas. A cold front likely moves through Thursday afternoon or evening, increasing chances of rain Thursday afternoon to as much as a low to medium (20- 50%) chance Thursday night into Friday morning as winds shift to northeasterly along with moderate seas. Gentle to moderate southeasterly winds and slight to moderate seas resume Sunday before another possible weak cold front and low chance of unsettled weather arrive into the beginning of next week.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 78 96 79 92 / 0 0 0 30 HARLINGEN 75 99 77 92 / 0 0 0 40 MCALLEN 79 101 79 94 / 0 0 0 50 RIO GRANDE CITY 76 100 78 92 / 0 0 0 40 SOUTH PADRE ISLAND 77 86 78 84 / 0 0 0 10 BAYVIEW/PORT ISABEL 76 95 78 89 / 0 0 0 30

BRO WATCHES/WARNINGS/ADVISORIES

TX...Heat Advisory from 1 PM to 7 PM CDT Wednesday for TXZ251-253>255.

GM...None.