textproduct: Houston/Galveston

KEY MESSAGES

- The Flood Watch has been expanded to now include Polk, Trinity, San Jacinto, Walker, Grimes, and Washington counties and is now in effect through late Monday.

- 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 306 PM CDT Fri May 22 2026

As we head into the late afternoon hours, focus turns towards potential for thunderstorm development, especially during peak daytime heating. Current thinking is for the convective temperature to be reached somewhere in the 4 to 7 pm time frame. The severe weather risk is low, but any strong storms could be capable of producing gusts up to 40 mph.

The forecast for this Memorial Day weekend remains on track. Southwesterly flow aloft will continue to bring multiple vorticity maxes/disturbances across the region tonight into at least early next week. At lower levels, persistent south-souteast flow continues to filter in a warmer and very moist airmass further inland. In fact, PWAT values are near or above the 90th percentile of climatology for this time of year. With that being said, the environment continues to be favorable for periods of showers and thunderstorms, some locally moderate to heavy. Confidence is high that periods of showers and thunderstorms will move through the region from Saturday through early next week. However, confidence in specific details regarding the timing and location of the heaviest rain amounts is still moderate, given the nature of these types of mesoscale features.

Speaking of confidence, some hi-res guidance brings an MCSs close to our region overnight through Saturday morning. Confidence in its occurrence is low to moderate; however, the environment continues to remain favorable for any convection. The passage of this MCS could either lower PoPs on Saturday or enhance the activity during the day when combined with daytime heating and any outflow boundary (- ies). The next best round of showers and storms returns on Sunday with another MCS moving in from our south. Additional rainfall amounts of 2 to 4 inches can be expected through late Monday. Isolated higher amounts of 5 to 6 inches will be possible. Rainfall rates are expected to peak in the 3 to 4 inches per hour range in the heaviest downpours.

The Flood Watch has now been expanded to include counties north of I- 10 and is now in effect until late Monday night. WPC highlights this threat in their Day 2 and 3 excessive rainfall outlook with a slight risk (level 2 of 4). In terms of severe weather, some of these storms could become strong to marginally severe on Saturday if the environment remains unstable in the afternoon. Damaging winds will be the main risk.

Forecast rainfall amounts have trended lower for Monday. While the upper level pattern remains active with continued southwesterly flow aloft, most models are suggesting some drier air will filter in from our west. Will continue with some diurnally driven isolated to scattered activity mainly for the afternoon and evening. The next period to monitor will be Tuesday into Wednesday as another strong disturbance moves through potentially bringing more rounds of moderate to heavy rain. We will provide more details on this system earlier in the week.

JM

AVIATION

(00Z TAF Issuance) Issued at 623 PM CDT Fri May 22 2026

VFR conditions currently across the SE Texas area along with S-SE winds at 4-12 KTS. A mix of VFR-MVFR cigs are expected overnight into early Sat morning and some sites could have vis reductions due to the development of patchy fog. Fog, if any, is expected to burn off around 15Z. Winds will be less than 5 KTS for most locations overnight, then 5-10 KTS after 14Z.

A few rounds of showers and thunderstorms are expected for much of the day Sat as a mid-upper level disturbance moves into Texas. Model guidance has not been performing will with the timing and placement of shower and thunderstorm activity these past few days, and we still see a few differences in the latest model runs for tomorrow's activity. Thus, I have placed PROB30s and TEMPOs for this TAF set, but we might be dealing with several AMDs as the event unfolds. Some strong storms will be capable of producing strong VRB wind gusts. Llvl wind shear may also occur along with llvl turbulence. SPC has placed a Marginal Risk (level 1 of 5) of severe thunderstorms, mainly for strong winds and hail.

There might be a few hours during the late evening/early night period where activity decreases a bit, however, we might still be affected by additional showers and thunderstorms rolling in during the overnight period.

Cotto

MARINE

Issued at 306 PM CDT Fri May 22 2026

Light onshore winds and low seas will continue this weekend and persist through the upcoming week. Scattered to numerous showers and thunderstorms is expected over the next several days. Locally heavy rain will be possible. The main concern will be strong winds and elevated seas with any strong storms.

JM

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) 70 82 68 80 / 40 80 60 60 Houston (IAH) 74 84 71 81 / 20 80 80 70 Galveston (GLS) 76 85 75 83 / 20 60 90 80

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.