textproduct: Houston/Galveston

KEY MESSAGES

- A Flood Watch remains 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 1136 PM CDT Thu May 21 2026

An active weather pattern is expected to prevail through next week as several mid to upper level disturbances pass through TX. For tonight through Friday morning, although some isolated spots could see a light shower or two, we are expecting it to remain mainly warm and humid. During the mid/late morning to the afternoon hours on Friday, we are expecting to have shower and thunderstorm activity increase from the coasts and expand northward as diurnal heating peaks, instability increases and a few vort maxes pass through. Speaking of heat, it will remain rather humid on Friday with highs in the mid to upper 80s and heat indices in the lower to mid 90s. Rain activity will decrease Friday evening as we loose the diurnal heating. There will be storms developing to our north, thus, we will need to keep an eye for the possibility of these storms rolling into the Brazos Valley and Piney Woods region.

Conditions are expected to get more active Saturday into Sunday. This is due to an upper level trough moving across TX that is to combine with PWs of near 2.0 inches, a saturated profile from the surface through the mid levels, the passage of multiple vort maxes, and CAPE values of 2-3K J/kg. This will lead to several rounds of showers and thunderstorms through much of the day and night. In addition to the locally developed activity, we might have the storms that developed to our north and west roll in, which can account for higher rain chances. For this forecast issuance, we have continued to carry numerous to widespread showers and thunderstorms Saturday morning into Sunday morning. With the amount of moisture that is to be in place, it will be of no surprise for moderate to heavy rainfall to develop (some showers could even produce rainfall rates of 2-4" per hour). Given that soils are fairly saturated from the rains we have received over the last few days, it will not take much for heavy rainfall to cause runoff and/or flooding impacts - in particular over the coastal areas. For that reason, a Flood Watch will continue in effect through Monday. The Watch is currently for most counties south of I-10 and west of I-45, however, it may be expanded based on where these heavy rains set up. WPC continues a Slight Risk (level 2 of 4) for all of Southeast TX valid from 7 AM Saturday through 7 AM Sunday. Some locations may be upgraded to a Moderate Risk (level 3 of 4) later today.

The environment will remain favorable for additional showers and thunderstorms on Sunday as another upper level trough pushes across TX. We continue to carry numerous to widespread showers and thunderstorms, although the heaviest activity could be situated over areas near and south of I-10 and east of I-45. But let's not sleep on that given that the placement of activity could end up either more north or even over the waters. Unfortunately, the Hi-Res models have not been performing too well lately. From 7 AM Sunday through 7 AM Monday, the Slight Risk will continue over locations near and east of Galveston Bay and a Marginal Risk (level 1 of 4) will cover the rest of Southeast TX. Again, because there is uncertainty of the exact location of the heavy showers, please make sure to monitor the radar and latest forecast updates and have multiple ways of receiving weather warnings. Make sure to check the traffic conditions before departing and never cross flooded roads.

Slightly lower chance for rain is expected Monday (Memorial Day) as the air dries a bit. However, we might have a few vort maxes still making their way through and sufficient instability for scattered showers and thunderstorms. Even if the potential for heavy rainfall ends up being less, even moderate rain can lead to minor flooding impacts over those areas affected by heavy rainfall from Saturday and Sunday.

Unfortunately, we are likely looking at rain chances each day through the rest of the work week as the "trough pattern" prevails aloft. Not sure if we will get a good day to cut our front yard forest :/

Stay tuned for more.

Cotto

AVIATION

(12Z TAF Issuance) Issued at 705 AM CDT Fri May 22 2026

Patchy fog development will continue across parts of the area for the next couple of hours. Next fairly weak shortwave and remnant light precip coming out of Mexico should make it into our southern terminal (IAH southward) in the 20-00z timeframe Fri. Unsure on overall coverage so maintained PROB30s in the TAFs. Otherwise, VFR with SCT to OVC high clouds and light southeast winds.

Bailey

MARINE

Issued at 1136 PM CDT Thu May 21 2026

Light south to southeast winds with seas of 2-4 feet are expected through early next week. Multiple rounds of showers and thunderstorms are expected for the next several days and although there currently isn't a severe threat, elevated winds and seas may still occur in and around strong thunderstorms.

Cotto

HYDROLOGY

Issued at 143 PM CDT Thu May 21 2026

Multiple rounds of moderate to heavy rainfall are expected through at least Monday. Areas along the coast, especially Matagorda and Brazoria Counties, received 5-8" over the past 48ish hours. The next round of rain is expected to move in either late this evening or Friday morning. Some of this rainfall may occur along the coast, which brings the potential for flash flooding. As a result, a Flood Watch continues for coastal counties through Monday morning. The Flood Watch will likely be extended northward and eastward within the next 24 hours to cover the threat area for the Saturday into Sunday timeframe of concern.

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. 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 we go into the weekend, 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 over the holiday weekend as intense rainfall rates will bring accumulated values of 4-6+" across most of Southeast Texas through 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) 85 71 82 68 / 30 20 80 70 Houston (IAH) 87 74 84 72 / 50 20 80 90 Galveston (GLS) 85 79 85 76 / 30 10 60 90

HGX WATCHES/WARNINGS/ADVISORIES

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

GM...None.