textproduct: Houston/Galveston

SYNOPSIS

Issued at 437 AM CDT Wed Jun 11 2025

Rounds of storms continue to make their way through the region as the week goes on, and the persistent, unsettled pattern will begin to add up as time goes on. Some of the key points from tonight's forecast: - A flood watch has been issued for portions of Southeast Texas north of the Houston metro. The initial locations of greatest concern will be streets and low-lying/poor drainage spots in more urbanized locations like Bryan/College Station and Huntsville. As the day wears on, accumulating rain may begin to result in flooding concerns beginning to emerge in more rural locations of the watch area. This area is in a moderate risk of excessive rain (threat level 3 of 4) today. - The rest of Southeast Texas, while not (yet) in a watch, will not escape cleanly. More isolated flooding issues may emerge in highly urbanized locations or places that have seen heavier rain the past couple days. The rest of Southeast Texas is in a slight risk of excessive rain (threat level 2 of 4). Depending on how today's rains evolve, there may be a need to expand the flood watch into parts of this area. - Finally, flooding caused by heavy rain is not our only concern today. There is also a marginal (threat level 1 of 5) to slight (threat level 2 of 5) risk of severe thunderstorms today as well. The primary threat is roughly along the I-10 corridor, where damaging wind gusts are the most probable hazard though a brief tornado or two can't be ruled out. A secondary hazard area-wide is also potential for large hail to around an inch in diameter.

SHORT TERM

(Today through Thursday Night) Issued at 437 AM CDT Wed Jun 11 2025

Our next round of showers and thunderstorms has moved out of Central Texas and is at our doorstep, primed to bring more rain and lightning to the area, along with some potential for flash flooding and severe weather.

To that end, we have a flood watch for the northernmost two rows of counties in our warning area. I was actually very on the fence about this watch, and nearly opted not to issue one. Why not? Well, unlike our neighbors, we've actually been fairly lucky with our rain so far this week. By and large, storms have been decently spaced out, and broad averages of rain totals are so far lower than those around us. While strong storms have put down heavier rain in isolated locations, by and large the area is in pretty good shape. We'll need to continue to get solid rainfall amounts to eat away at the cushion we have in our moist, but not yet saturated grounds.

So, when it comes to this watch, it's a bit of an evolving/fluid threat. Initially, the concern will be for urban locations in the watch area, particularly B/CS and Huntsville. Here, high rain rates from the strongest storms will have rain most quickly convert to runoff and could cause street flooding and/or flooding in low- lying and poor drainage areas. In fact, this potential is what finally pushed me to issue the watch. HREF probabilities for 1" per hour are above 50 percent and 3" per three hours above 30 percent (which I mentally round to 3" per hour, as this rain will be convective and likely concentrated in time) are found today in the watch area. Since heavy rain looks likely and there is a definitely signal for very heavy rain, those urban spots could see problems emerge and warnings needed before we could get a watch if out if we opted for a wait and see approach right now. As the day wears on, and potentially continues into Thursday...rain accumulations will begin to sap whatever cushion more rural areas have, and ultimately we could see a flash flooding threat emerge more broadly across the watch area.

One thing I want to really emphasize though, is that this is an initial effort at a flood watch. Even though other parts of the area are not currently under a watch, we are also keeping an eye on how rains perform there as well - especially the heavily urbanized Houston metro. Depending on how rain evolves today, and as we set our expectations through the rest of today into tomorrow, there may be some need to reconfigure the watch. I'm sure hoping we don't, but it's certainly on the table. One thing that stood out to me in the HREF probability-matched mean 3-hr QPF is that the signal for heavier rain did start to drift into the Houston metro. The difference between here and the watch area is that while we had a clear ensemble signal for heavier rain and potentially very heavy rain, the probabilities were much lower (and for very heavy rain, functionally gone). So folks south of the watch area should still be keeping an eye on how conditions evolve. And even if the watch can stay as it is, the flood threat is not zero outside the watch area. We could well see relatively lighter rains, but isolated flooding could still occur underneath one storm in particular. The broader threat may not be big, but it sure is in that one precise spot!

Beyond the flooding concern, there's also a severe threat to contend with. There is certainly some threat area-wide for storms producing damaging wind gusts and/or large hail, as we've had the past couple of days. All of Southeast Texas has at least a marginal risk of severe storms again today. I do want to focus on a corridor a little farther south, though. Objective mesoanalysis has MLCAPE already above 2500 J/Kg from around I-10 southward, and should modestly increase into the day, though cloud cover will thankfully keep it from increasing dramatically. Regardless, that's already enough to fuel some stout thunderstorms. Broadly speaking, bulk shear is not terribly impressive, but as we likely see the storms evolve into a mesoscale convective vortex as we saw with yesterday's storms, and the deformation of the low level wind field around that MCV should create a narrow area of enhanced deep layer shear. So, when you look at SPC's day 1 severe weather outlook and you see that narrow slight risk oval, that goes into why they're able to draw such a narrow alley. Where the instability lines up with this enhanced band of directional shear, that's where the potential for damaging wind gusts, and maybe even a brief tornado will emerge.

Beyond today...not much change for tomorrow. We wait for the next disturbance in the train to make its way through, and as we can pick out all the mesoscale details like we have today, we'll elaborate on the nuances. For now, the guidance seems to favor timing very similar to today: storms making their way in from the west in the morning, and scraping their way across Southeast Texas through the day. But so many of the details are subject to being modified by how today plays out, so be sure to check back for our latest thoughts.

LONG TERM

(Friday through Tuesday) Issued at 437 AM CDT Wed Jun 11 2025

The long term forecast continues to feature active weather with periods of showers and thunderstorms likely over the weekend into next week. Midlevel ridging near Baja California is progged to gradually shift E/NE and amplify over the next several days, though it'll remain distant enough such that a few disturbances & shortwave impulses will be able to wedge their way south and pass through the region. With deep moisture and high PWs of 1.8-2.4 inches still expected, there will be a daily risk of heavy downpours. WPC maintains a Slight (level 2/4) to Marginal (level 1/4) risk of Excessive rainfall on Friday into Saturday, and may likely extend this risk through Sunday into early next week. Additional rainfall amounts from Friday through Tuesday will generally be under 1 inch, though isolated higher amounts will be possible each day, especially in areas further north/northeast. Rainfall from earlier this week will likely increase soil saturation, make them more prone to runoff. Rises in creeks and streams are likely as a result. Minor to Moderate river flooding is still ongoing over portions of the Trinity river and will likely continue as a result of this additional rainfall.

AVIATION

(06Z TAF Issuance) Issued at 1135 PM CDT Tue Jun 10 2025

Seeing a lull with rainfall this evening with quiet weather and VFR conditions prevailing overnight into the early morning hours of Wednesday. Seeing some cloud decks from 1500-3000 ft this evening with occasionally MVFR CIGS. Current thinking is that these CIGs will be more intermittent in nature, though longer periods of BKN CIGS cannot be fully ruled out throughout the pre- dawn hours. Expect more rounds of showers and Thunderstorms throughout the TAF period as several disturbances pass over the region.

Timing these rounds will be challenging, though models have shown some degree of consistency with them. The next round is set to occur during the 13-18z timeframe, though recent model runs have trended downwards in terms of the expected rainfall during this period. Consequently, this is translating to a more active period during the late afternoon/early evening, though again this hinges on how morning convection evolves. Afterwards, we'll likely see another lull in rainfall early in the evening before another wave of activity overnight/early Thursday morning. Some of these storms throughout the TAF period could produce strong wind gusts and locally heavy rainfall/low visibility. Lower cloud decks and occasional CIGS to MVFR levels can be expected Wednesday evening though the predawn hours of Thursday.

03

MARINE

Issued at 437 AM CDT Wed Jun 11 2025

Small craft should exercise caution early Monday morning for south winds of 15 to 20 knots and sea ranging from 3 to 5 feet. In Galveston bay, wave heights up to 2 ft have been reported with occasional wind gusts to 30 knots for higher-profile ships. A broken line of thunderstorms is expected to push off the coast around sunrise, briefly bringing strong wind gusts and northerly flow as it moves through.

Onshore flow prevails throughout most of the work week with speeds generally around 10 to 20 knots, warranting caution flags at times (mostly at night for higher gusts). Seas will range from 2-5 ft with a high risk of rip currents expected across gulf-facing beaches. Scattered showers and storms will be a daily possibility.

HYDROLOGY

Issued at 437 AM CDT Wed Jun 11 2025

Flood threats, both riverine and flash flood, are beginning to emerge around Southeast Texas as we enter the middle of a rainy week. Here's a quick summary of where things stand:

Flood warnings continue on the Trinity River at Liberty and Moss Bluff. Both of these points are expected to remain above flood stage for several days.

A flood watch has been issued for portions of Southeast Texas north of the Houston metro. The initial concern will be for thunderstorms producing excessive rain rates causing localized street flooding, and flooding of low-lying and/or poor drainage areas in more urbanized locations such as Bryan/College Station and Huntsville. As rain continues to accumulate, more rural areas may also see flooding threats emerge in high rain rate storms.

Additionally, depending on how rains materialize today, and our developing expectations for rain into Thursday, the flood watch may need to expand or move. Everyone in Southeast Texas will be well-served to keep up with the latest forecast information.

PRELIMINARY POINT TEMPS/POPS

College Station (CLL) 89 72 83 74 / 90 60 80 40 Houston (IAH) 91 76 88 78 / 80 50 70 30 Galveston (GLS) 88 80 87 82 / 50 40 40 30

HGX WATCHES/WARNINGS/ADVISORIES

TX...Flood Watch through Thursday morning for TXZ163-164-176-177- 195>198.

GM...Small Craft Should Exercise Caution through Thursday morning for GMZ330-335-350-355.