textproduct: Houston/Galveston

KEY MESSAGES

- Hot and humid conditions will continue through Wednesday.

- Periods of showers and thunderstorms are expected each day, peaking Thursday through early Sunday. Locally heavy rain will be possible and could lead to instances of flash flooding.

- The heavy rainfall threat shifts from the Brazos Valley on Thursday/Friday to the coast on Saturday/Sunday.

- Daytime temperatures are expected to drop to more seasonal levels in response to rain and increased cloud cover.

DISCUSSION

Issued at 1119 PM CDT Tue Sep 29 2026

Welcome back to the next novel in the Southeast TX forecast series. We'll keep the short term/long term theme going...along with a mini- bonus section at the end (if you read yesterday's discussion you know what it's about). The same thing applies where we'll keep most of the heavy rainfall discussion in the long term section, but definitely read both! Let's dive in...

Short Term {Thru Thursday Afternoon}:

As we discussed yesterday, moisture availability was greater west of I-45. When you pair that with a little bit of moisture convergence and daytime heating, you get isolated to scattered showers and most of that activity was generally west of I-45. So...that tracks! Moisture will continue to increase going into Wednesday with widespread PW values exceeding 2" (90th percentile: ~1.95"). This is important to note because a rather robust nocturnal LLJ will develop overnight into Wednesday morning over central TX stretching into OK in a south to north orientation. We'll be on the divergence side of this LLJ, so we have the lift and the moisture. As a result, rain chances are a bit higher and more widespread for Wednesday. With climatologically high amounts of moisture in place, we could see a few locally heavy downpours led to a few pockets of 1-2". HREF PMM points towards areas south of I-10 having the best potential for this occurrence. It's worth mentioning we did have a couple of spots get 1-2" of rain fairly quickly today, and there will be more moisture and greater lift on Wednesday...so you can do the math on that one.

High temperatures on Wednesday will still top out in the low to mid 90s, but with the added moisture in place it may feel just a teensy bit hotter. Heat indices will peak in the triple digits (mainly in the 102-107 degree range), so not anticipating any heat products to be issued at this time. Partly due to the scattered rain throughout the day, but also it'll be quite breezy as well. Wednesday will definitely be Winds-day, so let's talk about why! The pressure gradient tightens as surface low pressure develops near the NM/TX border and drifts northeastward. With surface high pressure situated over the eastern CONUS, we get put into a bit of a squeeze play leading to breezy southeasterly winds. Winds will be gustiest right along the coast especially Wednesday night, so I wouldn't be too surprised to see a Wind Advisory for the barrier islands during this time period.

The development of the aforementioned surface low pressure comes in response to an upper level trough and an embedded upper low that transitions through the southwestern CONUS. The remnants of Polo (currently in northern Mexico) will become embedded with this upper level disturbance by Wednesday morning. The most notable part of this though is that the moisture from Polo's remnants will become embedded with this trough as it continues to move eastward into TX. Going into Wednesday night, the nocturnal LLJ strengthens again this time stretching southwest to northeast from central TX to eastern OK. This keeps the main region of lift to our west, and this is a good time to mention that a slow-moving cold front will be gradually pushing southeastward through the northern/central parts of TX. So, the Wednesday night into Thursday heavy rainfall axis will be relegated to along the front and stretching a bit further southwestward into portions of the Hill Country (thanks to divergence aloft).

Going into Thursday, PW values will begin to peak above the MAX percentile (~2.3") for portions of the Brazos Valley and the Piney Woods. This is when we'll be closely monitoring the progression of the frontal boundary along with any embedded shortwaves. Still a very good chance of scattered showers/storms throughout the day. High temperatures will mainly be in the low 90s, so our main attention will be on the rain chances as they reach their first peak Thursday night into Friday.

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This halftime break is brought to you by the National Weather Service! Visit www.weather.gov/houston to stay up to date on the latest local forecasts for Southeast TX, but also be sure to visit www.wpc.ncep.noaa.gov to stay up to date on the latest Excessive Rainfall Outlooks and to see their very detailed discussions!

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Long Term {Thursday Night Thru Early Next Week}:

So, we left off with an axis of climatologically high amounts of moisture moving into our area as moisture converges along and ahead of a slow-moving frontal boundary. The primary timeframe of concern for heavy rainfall in portions of Southeast TX remains Thursday night into Friday. This is when we have the combination of PW values well above 2.0", embedded shortwaves, and potentially frontogenetic forcing lining up over portions of the Brazos Valley. The best potential for heavy rainfall remains to our northwest, but there's enough uncertainty remaining in exactly where the band of heavy rain sets up...this is especially true given the recent trends of the GFS. The 12Z and 18Z runs of the GFS depicted a cutoff low developing on the tail-end of the upper level trough, which hypothetically could push the heavy rain axis a teensy bit eastward. Some other deterministic guidance has weaker versions of this solution, so it's a possibility worth noting.

A further eastward heavy rain axis would increase the flash flooding threat for portions of the Brazos Valley. Rainfall rates could easily peak above 3-4"/hr in the heaviest downpours. These rainfall rates for an extended period of time can quickly lead to issues. While the best potential for this continues to remain to our northwest (Hill Country and DFW metroplex), there remains quite a bit of uncertainty. The forecast depends on the placement of the front, if the front stalls, if the subsequent cutoff low develops, does the cutoff low drift southward enough to push the rainfall axis southward, and more.

With all of that in mind, WPC has maintained the marginal to slight risk of excessive rainfall Thursday through at least Saturday for all of Southeast TX with the slight risk generally for western/northwestern areas on Thursday. There will likely be at least a marginal risk as well for Sunday. See the Excessive Rainfall Outlook graphics on either our webpage (www.weather.gov/houston) or WPC's webpage for specifics for your particular location.

In terms of rainfall totals, we are still anticipating widespread amounts of 2-4" with higher totals the further north and west you go. Locally higher totals are certainly possible especially in portions of the Brazos Valley. The aforementioned frontal boundary pushes through some time on Friday, but does look to linger just offshore. With PW values remaining near the MAX percentile, a nearby front, and embedded shortwaves, this brings us to our next peak for heavy rainfall late Saturday into Sunday mainly along the coast. This is the result of moisture converging along the front and a coastal trough/low in the northwestern Gulf. Keep in mind, this is a scenario where the bulk of the rainfall could also occur just off of the coast as well...a ~10-20 mile margin of error could make a big difference. Definitely stay up to date on the forecast as the weekend approaches and we get a better idea of how this part of the heavy rain event will play out. So, now you see how complex this forecast is as the flood threat transitions from the Brazos Valley late this work week to the coast over the weekend. Elevated moisture persists going into early next week, then things get a little confusing...we'll talk more about that in the section down below.

In terms of temperatures, the increased chances for showers/storms translates to high temperatures only topping out in the 80s after Thursday and some low temperatures in the 60s for some towards the end of the forecast period.

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Even Longer Term {Cold Front Hunting 2: Electric Boogaloo}:

I don't wanna get excited too early, but I'm liking the chances of a cold front next week (insert eyes emoji here). In the section above, I mentioned that things get a little confusing shortly after early next week. The general synoptic pattern remains the same with an an upper level trough dipping down into the northern/northeastern CONUS. A cold front will push through the eastern CONUS with a 1028- 1030mb surface high in its wake.

There is some potential for the tail-end of this front to push into our area in the early to middle part of next week bringing in cooler and drier air. A majority of ensemble members (both GEFS and Euro) reflect a decreasing trend in moisture, and quite a few show below normal low temperatures as well. Now again, this isn't an official forecast at this point, but it's nice to know that there's at least a chance! Yep, we're saying there's a chance! However, even if this front pushes through our area, it wouldn't be a substantial cooldown...but it would be noticeable nonetheless.

Batiste

AVIATION

(12Z TAF Issuance) Issued at 611 AM CDT Wed Sep 30 2026

Some isolated-scattered showers on the radar scope this morning. These will be possible throughout the day, but choosing any individual time period or location is difficult. Could theoretically mention some low probabilities for most terminals today, but overall significance/strength don't appear to be worth the mention at the current time. We'll keep an eye on the radar and amend as necessary. Otherwise, VFR conditions today with SE winds increasing toward mid morning with some gusts to or slightly above 20kt this afternoon. Gustiness should settle, except at the coast this evening. Looking like we'll see a mix of sct-bkn MVFR ceilings develop during the late night hours. 47

MARINE

Issued at 1119 PM CDT Tue Sep 29 2026

Moderate southeasterly winds and gradually building seas (peaking in the 5-8 ft range late Wednesday/early Thursday) will persist into Thursday. A Small Craft Advisory is in effect for the bays and Gulf waters through at least Thursday morning. Water levels during the latter half of the week will peak around or just above 3.0 ft MLLW, so not enough for coastal flooding hazards but high enough for mariners to take note. Daily chances of showers/storms continue especially during the overnight to early morning hours over the Gulf. Expect rain chances to increase after midweek as an upper level disturbance pushes into TX along with a slow-moving frontal boundary. Rain chances look to peak over the weekend for coastal areas and the Gulf as a frontal boundary and a coastal weather system interact.

Batiste

PRELIMINARY POINT TEMPS/POPS

College Station (CLL) 95 75 93 71 / 30 10 80 90 Houston (IAH) 93 79 92 77 / 50 10 70 50 Galveston (GLS) 89 83 89 82 / 30 10 60 50

HGX WATCHES/WARNINGS/ADVISORIES

TX...None. GM...Small Craft Advisory until 7 AM CDT Thursday for GMZ330-335-350- 355-370-375.