textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 640 AM CDT Wed May 27 2026

- A Marginal to Slight Risk (levels 1 and 2 of 4) of isolated to scattered flash flooding from excessive and heavy rainfall is outlined for portions of Deep South Texas today.

- Strong to isolated severe thunderstorms will continue into this morning and/or re-develop this afternoon. Primary threats are gusty winds, small hail, lightning, and locally heavy rain.

- A moderate risk of rip currents continues through Thursday evening.

- Minor to moderate heat risks (level 1 and 2 of 4) persist, peaking this weekend as dry conditions and clearer skies temporarily return.

DISCUSSION

Issued at 1039 PM CDT Tue May 26 2026

And once again, we are now staring down the barrel of another potential dark and stormy night here in deep south Texas. A deep and negatively-tilted mid/upper level trough persists overnight across northern and eastern TX, downstream of a strong trough/cut-off low aloft digging southward over the western US. The combination of Pacific (via southwesterly 700 mb flow) and Gulf (via lower level southeasterly flow) moisture transport into the area of increased forcing for ascension aloft has resulted in numerous severe thunderstorms across western, central and southern Texas today and this evening, with the southernmost portion of activity currently producing a squall line extending south-southwestward from just east of San Antonio on down to Webb and Duval counties, just north of the Northern Ranchlands, generally moving due east. Meanwhile, overcast skies loom over our region along with dry conditions. The latest SPC Mesoanaylsis indicates 7.0-7.5 C/km mid-level lapse rates and 35-45+ kt bulk shear across most of the region as well as SBCAPE and MUCAPE values of 3,000-4,000 J/kg (highest along/west of US-281) in addition to 500 mb analysis showing the best upper level flow divergence across the Northern Ranchlands, all of which is setting the stage for strong to severe thunderstorms anticipated over the coming hours.

The HRRR continues to be more or less the best in accurately initializing the latest regional conditions/radar and this evening's 00Z run indicates the area of developing convection over the Sierra Madre/northwest of Zapata County to intensify and lengthen southward, bringing the possibility of strong to scattered severe thunderstorms, potentially along another squall line, eastward into Zapata, Starr, Jim Hogg, Brooks and Kenedy counties late tonight, where there is a Severe Thunderstorm Watch effective until 6 AM Wednesday morning. The primary threats across this area continue to be damaging winds of 58-75 mph and large to very large (1-2 inch) hail. Although Hidalgo, Cameron and Willacy counties are not part of this watch due to less instability, conditions are still supportive for strong to isolated severe thunderstorms, still capable of producing strong to isolated damaging winds and small to isolated large hail. Additionally, as PWATs could surge to as high 2.0-2.30 in. overnight, these storms are likely to be efficient rainfall producers with the capability of easily producing 1-3+ inches where thunderstorms move slowly or train. Therefore, WPC maintains a Slight Risk of scattered flash flooding from excessive and heavy rainfall over the northern portions of Zapata, Jim Hogg and Brooks counties as well as a Marginal Risk for isolated flash flooding to as far south as southeastern Starr, northwestern Hidalgo and northwestern Kenedy counties.

Whatever is left of the convective activity by Wednesday morning should continue to move eastward and be mostly over the Gulf, possibly by mid-morning, followed by a low to medium (30-60%) chance of showers and thunderstorms in the afternoon and early evening hours. However, due to run-to-run model inconsistency in timing and convective mode(s), it is less certain for the prospects of severe thunderstorms either continuing in the morning and/or redeveloping in the afternoon. Yet, these aspects should gain more confidence overnight tonight as the convection unfolds. Still, high moisture content leads to a Marginal Risk of isolated flash flooding mainly along/east of US-281, as far west as the far eastern portions of Jim Hogg County and northern/eastern half of Hidalgo County.

Ridging resumes behind the departing trough Wednesday night with a dry stretch ensuing into the weekend, when troughing over Mexico and the Desert Southwest begin to bring some more daily chances of unsettled weather, possibly beginning Saturday night. Chances remain low to medium (20-40%) at this time, though could become more widespread and persistent by early next week.

High temperatures in the low/mid 90s, possibly upper 80s further north, continue through most of the next 7 days along with maximum afternoon heat indices ranging within a few degrees from 100-105 F. Mainly minor heat risks can be expected across most of the region each day though more urban areas of the RGV could experience moderate. As moisture and heat build again from southeasterly winds and increased sunshine late this week and into this weekend, a moderate risk could become more widespread across the RGV Friday into Saturday and across the rest of the region on Sunday before reducing to mostly minor early next week as cloud cover increases. Heat indices up to 110 F are possible within the moderate heat risks.

A moderate risk of rip currents continues through Thursday evening.

AVIATION

(12Z TAFS) Issued at 640 AM CDT Wed May 27 2026

MVFR ceilings and southerly to southeasterly winds around 10 to 15 knots are being observed across the TAF sites this morning. Meanwhile, a complex of showers and strong thunderstorms continue to translate across portions of the Northern Ranchlands and mid Texas coast. High res guidance indicates this activity should spread further south towards the TAF sites by mid morning, and exit the region by early to mid afternoon. Main threats with any thunderstorms will be gusty winds, small hail, reduced ceilings and/or visibility, lightning, and locally heavy rain. Brief wind shifts can also be expected within any strong thunderstorms. Conditions should improve later this afternoon, although intermittent periods of MVFR ceilings cannot be ruled out.

MARINE

Issued at 1039 PM CDT Tue May 26 2026

Small Craft Exercise Caution headlines, resulting from moderate to fresh winds and moderate (3-5 ft) seas are likely to continue through tonight before easing to mainly gentle to moderate easterly to southeasterly winds and slight to moderate (2-4 ft) seas for the remainder of the next 7 days. Chances of rain gradually increase throughout tonight to as much a medium (40-60%) chance Wednesday morning and gradually diminish to around 15% or less from Thursday into this weekend. Low to medium chances of rain return either late this weekend or early next week.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 90 77 92 77 / 40 20 20 0 HARLINGEN 90 74 91 74 / 50 20 10 0 MCALLEN 92 77 93 76 / 40 10 20 0 RIO GRANDE CITY 92 74 93 75 / 40 20 10 0 SOUTH PADRE ISLAND 85 80 85 80 / 40 20 10 0 BAYVIEW/PORT ISABEL 88 77 89 77 / 40 20 10 0

BRO WATCHES/WARNINGS/ADVISORIES

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