textproduct: Houston/Galveston

KEY MESSAGES

- The next upper level disturbance will be moving into the area from the west early this morning and across the area into early afternoon. A Flood Watch will remain in effect for counties along the coast through Monday morning.

- Multiple rounds of thunderstorms are expected through the holiday weekend and into next week. Some may be strong at times. Locally heavy rainfall is possible leading to the potential of flash flooding.

- Mariners should be prepared for the multiple rounds of storms. Winds and seas will be higher in and near storms.

DISCUSSION

Issued at 111 AM CDT Thu May 21 2026

Satellite imagery shows 2 areas of interest early this morning. An upper disturbance, and a few embedded stronger tstms, is pushing into the Hill Country. It's situated along a weak surface boundary and some modest upper diffluence aloft which is probably maintaining the stronger cells on its southern periphery. SPC mesoanalysis indicates this precipitation will be moving into a more stable airmass as it nears the Brazos Valley. So, assuming no substantial surprises between now and then...we'd generally anticipate some weakening as it approaches the local area.

The second area of concern is the disturbance moving into South Texas from Mexico. Guidance all generally agrees storms associated with this one should maintain themselves as they move into a more unstable environment. The uncertainty lies in the finer details...whether it mostly stays offshore...or, as some of the 00z hires models (NSSL, ARW, FV3, RRFS) suggest - taking an MCV on a bit of a more ENE route and up the upper Tx coast. I don't have a great feel on how this one evolves, but if the stronger northern route takes shape this batch of storms may make it to the Matagorda Bay area around or shortly before sunrise then track NE across the remainder of the area during the day. A Flood Watch remains in effect for coastal regions from last nights heavy rain. Additional heavy rain in a short period will be prone to quickly runoff and produce some flooding. If the southern trajectory ends up being the way it decides to go, expect less overall coverage across the region and lesser amounts. There is a weak pseudo coastal trof/boundary near the coast leftover from last nights convection to watch for some focusing.

Otherwise, not much to add that hasn't already been said. Pattern will be favFM220600 VRB05KT P6SM BKN025orable for additional rounds of showers and tstms...especially this weekend (and quite possibly into a good part of next week) as the western mid-upper trof and associated disturbances slowly track toward and into Texas then put on the brakes for several days. It's not a good pattern to be in this time of year and appears to be a somewhat prolonged favorable heavy rain setup for this region. Though confidence on the overall pattern/rain chances is above average...confidence in regards to specific timing and rain amounts are fairly low. With each additional bout of rain, the soils will become increasingly saturated and have less ability to absorb the precipitation...and the corresponding risk of flooding/flash flooding will increase. When deterministic data points at an additional 4-6" by midweek, we all know some isolated locations can receive much higher amounts, in a much shorter amount of time, this time of year. Residents should keep up with the latest weather forecasts. 47

AVIATION

(12Z TAF Issuance) Issued at 612 AM CDT Thu May 21 2026

Heavy SHRA/TSRA over S TX may extend as far north as our coastal zones this morning, potentially impacting GLS and LBX. For the Houston area, we expect some SHRA this morning, with the best chance of steadier rainfall south of I-10. The afternoon forecast is highly uncertain. May see some diurnal SHRA/TSRA activity early afternoon, as well as late afternoon/early evening near a stalled boundary to our north (more applicable to CLL and UTS). The next disturbance may not arrive until tomorrow morning. It is uncertain as to whether or not it will bring widespread SHRA/TSRA or be limited to southern / coastal areas like this morning.

MARINE

Issued at 111 AM CDT Thu May 21 2026

The next weather disturbance will be pushing off the mid and lower Texas coast overnight. The northern periphery of this storm complex could track across portions of the upper Texas coast between about 5am and noon, though timing of storms remains a bit uncertain. Mariners should check the latest forecast and weather conditions before beginning or continuing their transits. Multiple rounds of showers and thunderstorms are anticipated through the holiday weekend, so take note of the potential for intermittent periods of elevated winds and seas in and around any of the stronger thunderstorms. Outside of the storm complexes, expect light to occasionally moderate onshore flow with 3-5 ft seas. 47

HYDROLOGY

Issued at 230 PM CDT Wed May 20 2026

Multiple rounds of moderate to heavy rainfall are expected through at least Monday. Areas along the coast, especially Matagorda and Brazoria Counties, received 4-6+" between the rounds of rainfall Tuesday night into Wednesday morning. These areas are expected to see another round of moderate to heavy rainfall on Thursday and Friday, which brings the potential for flash flooding. As a result, a Flood Watch was issued for coastal counties for Thursday morning through Monday morning. The current extent of this Flood Watch includes areas with a flood threat within the next 24-48 hours, so the watch could be expanded in area as the rainfall threat evolves going into the weekend. With PW values near or above the 90th percentile (~1.79") through the weekend, rainfall rates are expected to peak in the 3-4+" per hour range in the heaviest downpours. Additional rainfall totals through Friday are anticipated to be in the 2-4" range along the coast. Through Monday/Memorial Day, expecting widespread 4-6" rainfall totals with isolated higher amounts.

Anywhere we see these intense rainfall rates, localized flash flooding is possible. That being said, we are not anticipating widespread river flooding just yet; however, this will help prime the soils as we continue with a wet pattern. As the week progresses, multiple rounds of moderate to heavy rainfall on top of primed soils will generate runoff and cause rises on area rivers and watersheds. The greatest threat for heavy rainfall, flash and riverine flooding comes this holiday weekend as intense rainfall rates will bring accumulated values of 4-6+" across most of southeast Texas into Monday.

Widespread action to minor stage flooding is expected with moderate to isolated major stage flooding possible depending on where the most rainfall accumulates. Remember that you can monitor updated river forecasts via the NWS NWPS webpage (https://water.noaa.gov/).

Batiste/Landry-Guyton

PRELIMINARY POINT TEMPS/POPS

College Station (CLL) 80 69 85 71 / 60 30 40 20 Houston (IAH) 80 71 86 74 / 80 40 60 20 Galveston (GLS) 81 77 83 78 / 80 30 60 20

HGX WATCHES/WARNINGS/ADVISORIES

TX...Flood Watch through Monday morning for TXZ226-227-235>238- 335>338-436>438.

GM...None.