textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 118 PM CDT Thu May 21 2026

Key Messages:

- Heavy rainfall with the potential for flash flooding will be a concern through the weekend. A Flood Watch is in effect through Monday morning.

- Another round of severe weather is possible this evening and overnight. The Storm Prediction Center has Zapata and western portions of Jim Hogg counties under a Marginal Risk (level 1 of 5) for severe weather. The primary hazards are damaging wind and large hail.

- Daily rain chances are forecast to continue into next week, with the highest probabilities for rain forecast to occur Saturday and Sunday.

DISCUSSION

Issued at 118 PM CDT Thu May 21 2026

An upper level trough looks to remain situated across the Western US, running along the Rockies into Northern Mexico. A series of embedded shortwaves will rotate through the southern periphery of the trough, amplifying forcing across Deep South Texas through the weekend. The strongest of these shortwaves, paired with a 250 MB jet streak will likely lead to strong upper level divergence and increased synoptic forcing over Deep South Texas Saturday.

At the surface, a stalled frontal boundary across Central Texas will likely remain stationary through Friday before retreating to the north going into the weekend. Easterly to southeasterly surface flow across Deep South Texas will continue to advect additional moisture into the region. PWAT values are forecast to peak on Saturday, generally ranging form 2 - 2.3 inches Saturday afternoon and likely exceeding the 90th percentile.

These factors will likely support multiple rounds of showers and thunderstorms through early next week. A Flood Watch is in effect for all of Deep South Texas through Monday morning. Another round of convection is possible this evening and overnight, however the latest CAMs suggest the convection may dissipate as it moves through the western to central portions of the CWA. Flooding will likely be a concern this evening for portions of Zapata, Starr, and Jim Hogg Counties that received 3-4 inches of rain with the storms this morning. Additionally, some of these thunderstorms could become strong to severe, with damaging wind or large hail possible. The Storm Prediction Center has Zapata and western portions of Jim Hogg counties under a Marginal Risk for sever weather this evening. Rain chances Friday afternoon will likely be limited to the eastern half of the CWA, and limited to around 20-30%.

The combination of synoptic forcing and elevated moisture values will likely support widespread showers and thunderstorms Saturday. Nearly all of Deep South Texas is under a Slight Risk for Excessive Rainfall (level 2 of 4), except for western portions of Starr and Zapata counties which remain under a Marginal Risk (level 1 of 4).

Rain chances will continue Sunday and Monday as the southern portion of the trough slowly moves across the State of Texas. Rain chances may briefly decrease Monday night into Tuesday, before the next trough moves into the the Southwest mid week bringing additional rain chances to the area.

AVIATION

(18Z TAFS) Issued at 118 PM CDT Thu May 21 2026

VFR conditions are forecast to continue through the afternoon, with MVFR conditions likely returning this evening. There is a low probability for showers and thunderstorms to develop overnight, however the latest HiRes guidance has these storms dissipating before making it to any of the TAF sites. As such, the probability for any thunderstorms are too low to include in the TAFs.

MARINE

Issued at 118 PM CDT Thu May 21 2026

Generally favorable winds and seas are forecast to continue through the period, however showers and thunderstorms will be possible daily, with the highest probabilities for storms around 60-70% over the weekend. Heavy rainfall, frequent lightning, and strong winds will be possible with any thunderstorms that develop or move over the water.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 77 91 78 91 / 20 20 20 50 HARLINGEN 73 91 75 92 / 30 20 30 60 MCALLEN 75 93 77 92 / 30 10 30 60 RIO GRANDE CITY 72 93 75 92 / 40 10 40 60 SOUTH PADRE ISLAND 79 85 80 85 / 20 10 20 40 BAYVIEW/PORT ISABEL 76 90 78 90 / 20 20 20 50

BRO WATCHES/WARNINGS/ADVISORIES

TX...Flood Watch through Monday morning for TXZ248>255-351-353>355- 451-454-455.

GM...None.