FXUS64 KBRO 200334 AFDBRO Area Forecast Discussion National Weather Service Brownsville TX 1034 PM CDT Tue May 19 2026 ...New DISCUSSION, MARINE... .KEY MESSAGES... Updated at 1031 PM CDT Tue May 19 2026 Key Messages: * Day-to-day or near day-to-day chances for showers and thunderstorms is expected through next weekend and possibly beyond amid a major shift in the weather pattern. * Strong to severe thunderstorms along with heavy rainfall and localized flooding is possible through next weekend. * There is a low-medium chance for showers and thunderstorms tonight into Wednesday morning; greatest chances over the Northern Ranchlands. * The Storm Prediction Center (SPC) has all of Deep South Texas under a Marginal Risk (Level 1 of 5) for severe thunderstorms with the exception of northern Jim Hogg and Zapata counties which is under a Slight Risk (Level 2 of 5). * The Weather Prediction Center (WPC) has our northwestern sections under a Marginal Risk (Level 1 of 4) for Excessive Rainfall Wednesday evening/night and all of Deep South Texas under a Marginal Risk for both Thursday and Saturday. && .DISCUSSION... Issued at 1031 PM CDT Tue May 19 2026 An increasingly active/wet weather pattern signifying a major pattern change from dry to wet remains the primary weather concern through the forecast period or through early next week. Through tonight and into Wednesday morning, we're tracking trends and the potential for showers and thunderstorms to develop as ongoing convection over Central Texas propagates southward along an outflow boundary. As of this update, there remains a low-medium (20- 60%) chance/confidence for showers and thunderstorms to develop and impact our region. As far as timing, the estimated time of arrival for storms is expected to be somewhere between midnight and 9 AM CDT Wednesday morning. One of the primary uncertainties is whether or not the MCSs/complexes of storms upstream across Central Texas will maintain it's momentum as it propagates southward through tonight into Wednesday morning. Some of the latest models favors a more eastward placement suggesting that most of the activity will pass to our northeast (i.e. Coastal areas of Corpus Christi) by Wednesday morning with maybe some stratiform showers/isolated thunder developing along or immediately behind the outflow boundary. Capping and the time of day could also serve as limiting factors in the magnitude of storms, especially further south along the Rio Grande Valley. That said, the best chances are across the Rio Grande Plains and the Northern Ranchlands tonight through Wednesday morning. The Storm Prediction Center (SPC) has maintained a Marginal Risk for severe thunderstorms though tonight into Wednesday morning for all of Deep South Texas with the exception of northern Zapata and Jim Hogg Counties, which are under a Slight Risk. A Marginal Risk for Excessive Rainfall has been applied to northern Brooks, jim Hogg, and Zapata counties. We'll continue to monitor trends through tonight and update as necessary. Wednesday through early next week, day-to-day or near day-to-day rain chances is expected. Driving this active pattern is an active southwest flow aloft sub-tropical jet in which multiple impulses/shortwave energies tracking over the Sierra Madre, and a nearby frontal boundary to our north. Persistent southerly flow near the sfc will continue to pool in deep tropical moisture helping to maintain high atmospheric water content through early next week. This is justified with sample maximum precipitable water (PWAT) values between 1.80-2.50 inches, some 1-3 STDEVs above normal and above the 90th percentile of sounding climatology for mid to late May. Furthermore, high instability values will be present through this week with steep mid level lapse rates between 6.5-8.0 C/km, SBCAPE values between 2,000-4,000 J/kg, MLCAPE values between 1,000-2,000 J/kg, a moderately to very unstable atmosphere with Showalter values ranging between -2 and -6. All in all, the combination of a favorable mid-upper level 500 mb steering pattern, high atmospheric moisture content, and high instability will support a noticeable change to a wetter/active weather pattern through the remainder of this week and possibly beyond. The best chances for rain this week looks to be on Thursday and then again over the weekend (i.e. Friday night through Sunday). Wednesday evening/night, 30-50% PoPs exist primarily along and west of IH-69C/US-281. Thursday-Thursday night, 30-60% chances exists with widespread categorical chances (50-60%) for showers and thunderstorms exists during the day on Thursday, and over the Northern Ranchlands and areas along and west of IH-69C/US-281. Meanwhile, 30-50% chances exists over the mid-lower Rio Grande Valley on Thursday. Friday night through Sunday, PoPs range between 40-70%. Additional chances (to a lower extent; between 20-50%) exists through early next week. Strong to severe thunderstorms are possible given the atmospheric and forcing ingredients highlighted above. However, heavy rainfall will be the primary threat. Given the high atmospheric moisture content available, heavy rainfall and instances of flooding is possible through next weekend. This is especially true for slow moving thunderstorms that repeatedly track over the same areas. The Weather Prediction Center (WPC) has our northwestern section (i.e. Zapata, Jim Hogg, Starr, and northwestern Brooks) under a Marginal Risk (Level 1 of 4) for Excessive Rainfall for Wednesday Night and all of Deep South Texas under a Marginal Risk (Level 1 of 4) for Excessive Rainfall for both Thursday and Saturday. Through Saturday, quantitative precipitation forecasts (QPF) or rainfall amounts are still expected to range between 1-2 inches with locally higher amounts across Deep South Texas and the Rio Grande Valley. The rain to come will certainly prove to be beneficial, helping to further improve the D1 (Moderate) to D2 (Severe) Drought status across the region. Temperature-wise, the combination of the heat ridge relaxing and day-to-day storm chances will allow for temperatures to run near normal levels for late May. Through early next week, high temperatures will generally range between the upper 80s to lower 90s. Overnight lows will run slightly above normal with readings mainly in the 70s (lower 80s Cameron County and over SPI). && .AVIATION... (00Z TAFS) Issued at 549 PM CDT Tue May 19 2026 Through 00z Thursday....VFR-MVFR conditions will prevail through the 00z TAF cycle. VFR conditions will be more prevalent during the afternoon-evening hours with MVFR conditions more prevalent during the night-morning hours. Showers and thunderstorms are possible tonight in association with a squall line that will be approaching from central Texas. Currently, there is still quite a bit of uncertainty in whether or not those storms make it into the Rio Grande Valley. That said, at this time, have not included shower or thunderstorm headlines in the TAFs. Southeast winds will continue through the forecast period with speeds between 8-13 knots and gusts as high as 20-25 knots. && .MARINE... Issued at 1031 PM CDT Tue May 19 2026 Adverse (Small Craft Exercise Caution) conditions will persist through Thursday evening. Friday through early next week, moderate seas along with light to moderate winds are expected. Daily or near daily shower and thunderstorm chances will be around through the forecast period. && .PRELIMINARY POINT TEMPS/POPS... BROWNSVILLE 80 9280 91 / 10 10 10 30 HARLINGEN 78 92 76 91 / 20 10 10 50 MCALLEN 79 94 78 92 / 30 20 20 50 RIO GRANDE CITY 77 94 75 91 / 40 40 40 50 SOUTH PADRE ISLAND 81 85 81 85 / 20 10 10 30 BAYVIEW/PORT ISABEL 80 90 79 89 / 20 10 10 40 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ SHORT TERM...23-Evbuoma LONG TERM....23-Evbuoma AVIATION...23-Evbuoma