textproduct: Houston/Galveston

KEY MESSAGES

- A Flood Watch will go into effect for counties along the coast Thursday morning through Monday morning.

- Multiple rounds of thunderstorms are expected through the weekend. Some may be strong at times. Locally heavy rainfall is expected at times 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 230 PM CDT Wed May 20 2026

With the threat for additional rounds of moderate to heavy rainfall going into the holiday weekend, there are naturally a lot more eyes on the forecast. With that in mind, I'll be tailoring this discussion mainly to what's expected and what are the potential impacts as a result of that...so I'll try not to use any complicated weather jargon this time around. Your main takeaways should be to stay weather aware by keeping up with the latest forecasts and have multiple ways to receive alerts (especially if you plans to be out on the road for the holiday weekend). Let's begin.

There were two rounds of showers/storms between Tuesday evening and Wednesday morning resulting in 3-6+" of rainfall along the coast (especially in Matagorda and Brazoria Counties). High-res model guidance is mostly in consensus on the next round of showers and storms moving through Thursday morning mostly along the coast. This rain is expected to move over areas that received the bulk of the rainfall last night/this morning. As a result, we decided to move forward with issuing a Flood Watch that extends from Thursday morning to Monday morning for counties along the coast. For additional details on the Flood Watch, see the Hydrology section below.

The good news is the remainder of the day today is anticipated to be on the dry side. That being said, we are starting to see some breaks in the clouds out to the west so can't entirely rule out some isolated to scattered showers/storms later this afternoon. The latest HRRR does show some spotty convective activity within the next few hours near and south of I-10. As we talked about above, the next round of the more widespread variety of showers/storms is "expected" to be Thursday morning. I included parentheses because timing these shortwaves (disturbances) can be tricky as we saw last night. High resolution model guidance shows the most of this rainfall occuring along the coast. There remains some uncertainty on the timing of shortwaves (disturbances) beyond that, but we are anticipating that they'll keep pushing into the area with an upper level low gradually approaching from the west going into the weekend. We'll have to monitor the progression of this upper low as it moves into Southeast Texas early next week (potentially moving overhead by Monday/Memorial Day). PW values will remain near or above the 90th percentile (~1.79") into early next week, so moisture availability will not be an issue in the slightest. Some of these storms may be strong at times carrying the potential for strong winds.

With all of that in mind, there is daily potential for locally heavy rainfall. We ended up creating a four panel Excessive Rainfall Outlook graphic to give y'all an idea of how long the heavy rain threat extends for...and that's not even including Day 5 (Sunday). This will likely extend into Monday/Memorial Day as well, so just know that we alternate between a marginal risk (level 1 of 4) and a slight risk (level 2 of 4) each day going into the weekend, but this is subject to change once we gain confidence on timing/location of the heavy rainfall potential. As far as rainfall totals go, we're anticipating widespread amounts of 4-6" with isolated higher amounts for Thursday-Monday. Keep in mind that these initial rounds of rainfall are priming the soils for the later rounds of rainfall. Saturated soils lead to quicker runoff, which brings the potential for flash flooding (hence the Flood Watch issuance). There is potential for the Flood Watch to be expanded in area going into the weekend, so be sure to stay up to date on the forecast for the latest details.

In case you wanted to know about the temperature forecast, it's going to be highly dependent on the timing of these rounds of rain. For now, we have high temperatures mainly in the low to mid 80s through next week but there may be times where the high temperatures remain in the 70s depending on timing of rainfall. Low temperatures will mostly be in the upper 60s to low 70s.

Batiste

AVIATION

(12Z TAF Issuance) Issued at 600 AM CDT Wed May 20 2026

Showers and thunderstorms are ongoing this morning, and continue to move east/southeast across the CWA. Based on the most recent model guidance, storms are expected to move southeast and exit the region by about 16Z. All sites prevail at VFR, with the main concern being the showers and thunderstorms ongoing this morning. Early this afternoon, CIGs are forecast to lower to MVFR for a brief period, before returning to VFR mid-afternoon. Winds will be about 5-10 KTs and variable today as the storms move through, eventually becoming southeasterly this afternoon. Near the end of this TAF period, another round of showers is expected to move in from west to east, although timing and the associated CIGs are uncertain. CIGs should lower, though it is uncertain whether they will lower enough to transition from VFR to MVFR. We will monitor trends in case amendments are needed.

MARINE

Issued at 230 PM CDT Wed May 20 2026

Multiple rounds of showers and thunderstorms are anticipated through the holiday weekend, so mariners should take note for the potential for intermittent periods of elevated winds and seas in and around any of the stronger thunderstorms that push through the waters. The next round of showers and thunderstorms is expected on Thursday morning. Timing of storms beyond that is a bit uncertain, but additional rounds are expected into at least Monday. Outside of the storms, expect light to occasionally moderate onshore flow with 3-5 ft seas.

Batiste

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) 70 79 70 83 / 40 80 50 50 Houston (IAH) 72 81 72 85 / 20 70 60 80 Galveston (GLS) 77 82 77 85 / 10 70 70 70

HGX WATCHES/WARNINGS/ADVISORIES

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

High Rip Current Risk through Thursday evening for TXZ436>439.

GM...None.