textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 538 AM CDT Thu Jun 18 2026

* Excessive Heat Warning is in effect for all of Deep South Texas, excluding the island from 11 AM to 8 PM CDT Thursday.

* Peak heat indices (feel-like) temperatures between 116-125F degrees will result in widespread Major (Level 3 of 4) Heat Risk on Thursday.

* Another hot day is expected on Friday with peak heat indices ranging between 100-120F degrees.

* Slight (low-medium) rain chances Friday night through Saturday night; best chances Brush Country.

* Very warm to hot and humid conditions will continue through the middle parts of next week.

DISCUSSION

Issued at 1044 PM CDT Wed Jun 17 2026

Very warm to hot and humid conditions will be the main weather storyline through the forecast period or through the middle parts of next week. The initial surge in the heat and humidity through Friday is stemming from the departure of Tropical Storm Arthur. The second surge in the heat next week will stem from a broad and anomalously strong 591-594 dam heat ridge. Through next week, mostly rain-free weather conditions can be expected as high pressure near the sfc and aloft will provide plenty of subsidence to stifle any rain chances (for the most part). Friday night through Saturday night will be our next best chances for any rain (lowest over the Lower Valley; highest over the Northern Ranchlands and west of IH-69C/US-281).

Tonight through Friday: In the wake of Tropical Storm Arthur, heat and humidity levels have and will continue to surge. Thursday will be the epicenter of this heat event. That's when daytime high temperatures are progged to climb into the upper 90s to mid 100s under sunny to mostly sunny skies. When you factor in the humidity levels with dewpoints in the upper 70s to lower 80s, peak heat indices or "Feel-Like" temperatures will climb into dangerous levels with values ranging between 116-125F degrees. This is some of the hottest temperatures in 2-3 years, since summer of 2024 and maybe even going back to the summer of 2023. These anomalously high temperatures will yield widespread Major (Level 3 of 4) Heat Risk on Thursday. Friday will be a rinse and repeat effort, though the heat will be slightly weaker compared to Thursday. High temperatures on Friday are expected to range between the mid 90s to near 100F degrees. This will result in peak heat indices ranging between 110- 120F degrees, which will result in Moderate (level 2 of 4) to Major (Level 3 of 4) Heat Risk. Another heat warning or advisory may be needed. Temperatures tonight through Friday night will provide little to no relief in the heat with overnight lows holding mainly in the lower 80s.

Saturday: There will be a slight reprieve in the hot temperatures on Saturday (still very warm however) as the heat ridge weakens (slightly). The slight weakening of the ridge could open up the door for shower and thunderstorm chances Friday night through Saturday night. Currently, we have low-medium (20-40%) rain chances Friday night over Jim Hogg, Starr, and Zapata Counties. On Saturday, we have low-medium (20-40%) chances for diurnal showers and thunderstorms across much of Deep South Texas (lowest Lower Valley and highest across Brush Country). Finally, Saturday night, we have low-medium (20-40%) chances for showers and thunderstorms over Jim Hogg, Starr, and Zapata Counties. Given the potential for additional cloud coverage and showers/storm prospects amid the brief 500 mb ridge weakness, high temperatures will be slightly lower than prior days (possibly the coolest of the forecast period) with values in the low to mid 90s. Peak heat indices will range between 100-112F degrees. Still, a Special Weather Statement (SPS) may be needed on Sunday. Little to no relief from the heat is expected with overnight lows Saturday mainly in the lower 80s.

Sunday through Thursday of Next Week: Forecast models and ensembles are depicting the heat ridge expanding over the southern U.S. and strengthening Sunday into next week. With a strong 591-594 dam heat ridge emerging over the region, very warm to hot temperatures will continue. We'll continue to keep an eye on the heat trends, but so far daytime highs are expected to re-emerge into the mid to near 100F degrees Sunday through Thursday of next week. During this time, the combination of the heat and humidity will result in peak indices ranging between 100-115F degrees each day. Additional heat advisories may be needed. Little to no relief from the heat is expected with overnight lows Saturday mainly in the lower 80s.

AVIATION

(12Z TAFS) Issued at 538 AM CDT Thu Jun 18 2026

Light southeast winds with some low stratus and patchy fog across portions of Deep South Texas early this morning. Latest satellite images and surface observations indicate some reduced visibilities and low ceilings leading to MVFR conditions at MFE and HRL. A mix of VFR/MVFR conditions will likely continue for the next few hours with full VFR conditions expected to return mid to late morning. Southeast winds between 6 to 12 kts early this morning will increase and become breezy later this morning with some gusts around 25 kts in the afternoon. MVFR conditions may return late in the period, mainly after 04Z.

MARINE

Issued at 1044 PM CDT Wed Jun 17 2026

Adverse to hazardous marine conditions will prevail through the forecast period or through next week. Mainly Small Craft Exercise Caution (SCEC) conditions can be expected, but there could be periods of high end SCEC to low end Small Craft Advisory conditions, particularly Thursday evening into Friday and again late Saturday into Monday morning.

CLIMATE

Issued at 1044 PM CDT Wed Jun 17 2026

Following the passage of now Tropical Storm Arthur, hot and humid conditions have emerge over Deep South Texas and the Rio Grande valley. A record high of 98F degrees was tied at KBRO on Wednesday. This tied with the years 1900, 2011, and 1989. Additional heat records are possible on Thursday, specifically over KBRO and KHRL. Below is a list of the record highs for Thursday June 18.

Record Highs for June 18:

Brownsville: 98F degrees (2012, 1934, and 1896) Harlingen: 102F degrees in 1934 McAllen: 105F degrees in 2023

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 97 84 96 84 / 0 0 0 0 HARLINGEN 99 81 96 81 / 0 0 0 0 MCALLEN 102 83 98 83 / 0 0 0 0 RIO GRANDE CITY 104 81 99 80 / 0 0 10 20 SOUTH PADRE ISLAND 91 85 90 85 / 0 0 0 0 BAYVIEW/PORT ISABEL 97 83 94 83 / 0 0 0 0

BRO WATCHES/WARNINGS/ADVISORIES

TX...Extreme Heat Warning from 11 AM this morning to 8 PM CDT this evening for TXZ248>255-351-353>355.

GM...None.