textproduct: Houston/Galveston

KEY MESSAGES

- Flood Watch remains in effect for most of SE Texas.

- Showers and thunderstorms are expected today. Some may be strong at times. Locally heavy rainfall is possible leading to the potential of flash flooding. Additional intermittent periods of rain/storms are anticipated Sunday and Monday for parts of the area.

- Mariners should remain weather aware this holiday weekend. Be prepared for higher winds/seas in and near storms and allow yourself plenty of extra time to return to shore before hazardous weather threatens.

DISCUSSION

Issued at 1241 AM CDT Sat May 23 2026

Upper low near Baja will make its way eastward this weekend. In advance, there will be multiple disturbances in the flow aloft to trigger shower/thunderstorm activity across the region. Guidance in these type of patterns is typically less than stellar in terms of specifics (timing, location, rain amounts, etc) and given the spread in incoming 00z model guidance, satellite, & radar trends...that generally holds true in this situation too.

There is considerable uncertainty how everything unfolds today. We currently have a string of eastward moving, n-s oriented, shortwaves stretching from the eastern Panhandle to the Hill Country to about the Big Bend area. Another, stronger looking, disturbance emerging west of Cabo tracking northeastward into nctl Mexico. In the low levels, if one squints hard enough, there is a little bit of speed convergence setting up along the upper Tx coast and some pooling 1.6-1.9" PW's. I think with the approach of the shortwave(s) and heating after sunrise, shra/tstms should blossom as the day progresses. Suspect everything will eventually be run on the mesoscale with boundary interactions, cold pools, etc....

In terms of the Flood Watch, considering the overall uncertainty, I don't think I could add any value with making adjustments. Generally speaking, model qpf's have been on a downward trend for a few days...now mostly forecasting 1-3" amounts (mostly south of a Livingston-Columbus line. However, some of the incoming 00z guidance is still advertising some VERY localized 4-7" amounts. NSSL WRF is the most concerning one I've seen so far...with a swath of high amounts across the coastal counties in the same spots that saw the high amounts the other day. There's a non-zero risk of some borderline strong/severe cells as well, but overall think rain rates and downpours will be the more significant risk.

Upper trof tracks into central Tx tonight, and into east Tx Sun-Mon. Continued chances of rain will persist, with the better chances east/southeast of where the trof axis is situated (say Matagorda Bay- Houston-Livingston or so). Would however think the overall coverage and amounts will be lower and will make downward POP adjustments Mon- Tue. Things might get active again toward midweek as the next western trof drops toward the Desert Southwest. 47

AVIATION

(06Z TAF Issuance) Issued at 1241 AM CDT Sat May 23 2026

Mid/upper disturbances will move across Texas tonight. These disturbances have already produced SHRA/TSRA in central and northern parts of the state. Most guidance shows this SHRA/TSRA activity dissipating overnight. While this scenario is possible, we are also noticing a fair amount of atmospheric instability across the region and cannot rule out overnight / early morning SHRA/TSRA in some of our terminals. For now, we have opted to add PROB30 SHRA to all TAFs for the early morning hours, while keeping TSRA in the TAFs for this afternoon. This forecast is very much in flux and future amendments are likely.

MARINE

Issued at 1241 AM CDT Sat May 23 2026

Look for maily onshore winds in the 10-15kt and 2-4ft seas to prevail through the holiday weekend, but with the disclaimer that wind directions, speeds and seas can and probably will be disrupted in and near several periods of thunderstorms. Pressure gradient tightens toward midweek with a corresponding increase in speeds & wave heights. 47

HYDROLOGY

Issued at 306 PM CDT Fri May 22 2026

Multiple rounds of moderate to heavy rainfall are expected this evening through Monday. The first round will start tonight bringing 2-4 " with isolated higher amounts of 5-6+". With PW values exceeding the 90th percentile (~1.7-2.1"), rainfall rates of 2-4"/hr are possible in the heaviest downpours. Anywhere we see these intense rainfall rates, localized flash flooding is possible. The greatest concern for the heaviest rainfall is Saturday afternoon through Sunday morning, but there is the possibly of heavy downpours through the entire weekend.

Rises to action to minor flood stage are likely though the weekend especially on flashier responding basins. Isolated moderate to major stage flooding is not out of the question depending on where the most rainfall accumulates. We will need to monitor area rivers and bayous over the next several days to see exactly where the heaviest rain falls. Remember that you can monitor updated river forecasts via the NWS NWPS webpage (https://water.noaa.gov/).

Going into next week, we will have monitor the forecast for additional moderate to heavy rainfall on top of primed soils as this will generate more runoff than normal. That being said, it is still too early to tell exactly which basins will have long term issues.

Landry-Guyton

PRELIMINARY POINT TEMPS/POPS

College Station (CLL) 84 68 83 68 / 60 50 40 30 Houston (IAH) 84 71 82 70 / 70 70 60 40 Galveston (GLS) 84 75 82 75 / 70 80 70 50

HGX WATCHES/WARNINGS/ADVISORIES

TX...Flood Watch through Monday evening for TXZ164-177>179-197>200- 210>214-226-227-235>238-300-313-335>338-436>439.

GM...None.