textproduct: Houston/Galveston

KEY MESSAGES

- Hot and slightly more humid conditions continue Tuesday with isolated coastal showers/storms.

- Periods of showers and storms are expected each day, peaking from Wednesday to Saturday. Locally heavy rain will be possible.

- Rain chances and increased cloud cover will keep temperatures near seasonal levels after midweek.

DISCUSSION

Issued at 1128 PM CDT Mon Sep 28 2026

There's quite a bit to talk about beyond midweek, so we'll split the discussion into two pieces...kind of a throwback to days of short term and long term. If you're mostly interested in reading about the heavy rainfall potential, you'll want to read the long term discussion. I'd suggest reading the short term one too though because that'll cover a couple of things that are important in the lead-up to the heavy rain...and I spent quite a bit of time on it too. Let's begin!

Short Term {Thru Wednesday}:

Palacios tied a daily record high temperature on Monday with hot conditions continuing going into midweek. There will be an ever so slight downward trend in temperatures over the next few days though as moisture gradually increases. Heat and increasing moisture is probably setting off some bells to check heat indices, but we're all good in that department. Lingering dry air east of I-45 will keep peak heat indices in the upper 90s in that region. West of I-45 is where the moisture initially increases, so heat indices over there will peak in the low to mid 100s...still low enough to not even think of a Heat Advisory. High temperatures area-wide will be in the low to mid 90s over the next few days. By Wednesday, low-level moisture will be elevated enough for widespread heat indices in the 100s and may flirt with the advisory threshold west of I-45.

Moisture is already on the rise well west of I-45/south of I-10 near Matagorda Bay. Some of you in this region received some rain earlier this afternoon, and you'll see some more again overnight and Tuesday. The latest CAMs (including me) still point towards this region seeing isolated showers early Tuesday morning then expanding in coverage going into the late morning and afternoon. Remember that drier air remains in place on Tuesday east of I-45...it wouldn't be impossible to see an isolated shower or two, but definitely way less plausible. Factoring in the tilted ridge axis overhead Tuesday doesn't make it any better either. Increased low-level moisture on Wednesday will lead to more widespread chances of scattered showers/storms.

Tuesday night into Wednesday will also feature breezy southeasterly winds as the pressure gradient tightens as surface low pressure develops near west TX/east NM. Wouldn't be too surprised to see a Wind Advisory along the barrier islands at some point on Wednesday (most likely Wednesday night). To segue into the long term, the development of the surface low pressure comes in response to an upper level trough and an embedded upper low transitions through the southwestern CONUS. The remnants of what is currently Hurricane Polo (making landfall in Baja California overnight) will become embedded with this upper level disturbance. Most notably, the moisture from Polo's remnants will become embedded with this trough and move eastward into TX.

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Long Term {Wednesday Night and Beyond}:

By Wednesday night, a slow-moving upper level low will begin to move into the TX panhandle. An axis of climatologically high moisture (PW values well above the 90th percentile [~1.95"]) will begin gradually nudging into portions of the Brazos Valley as moisture converges along and ahead of a slow-moving frontal boundary. Northern areas may catch the tail-end of a few embedded shortwaves late Wednesday into early Thursday, but the main timeframe of concern for heavy rainfall in Southeast TX remains late Thursday 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 that it'll be worth your time staying up to date on the forecast as confidence increases...especially for those of you in the Brazos Valley.

This is a pattern that favors locally heavy rainfall which can lead to instances of flash flooding especially in urban areas and low- lying areas. Rainfall rates could easily peak above 3-4"/hr in the heaviest downpours. The main question that remains to be answered (will become more clear with high-res guidance) is will we see prolonged periods of high rainfall rates in our area. As of right now, the "best" chance for this in Southeast TX is in the Brazos Valley, but again a lot of uncertainty remains. It all depends on where the frontal boundary is and if it stalls. The greatest potential remains to our northwest closer to the Hill Country and DFW metroplex. With that in mind, WPC has maintained the marginal to slight risk of excessive rainfall Thursday and Friday for all of Southeast TX with the slight risk generally for western/northwestern areas. See the graphics on our webpage www.weather.gov/hgx for specifics for your particular location.

In terms of rainfall totals, generally looking in the 2-4" range with higher totals the further north and west you go. Can't entirely rule out locally higher totals especially if the front sags further south Thursday night/Friday. The aforementioned frontal boundary pushes through some time on Friday, but elevated moisture persists through the weekend. That combined with embedded shortwaves also persisting means that chances for showers/storms remain in the forecast. On the plus side, this does translate to high temperatures only topping out in the 80s and some lows in the 60s toward the end of the forecast period.

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Even Longer Term {Cold Front Hunting}:

If y'all know me, then y'all know I'm always on the hunt for the first "real" cold front this time of the year. There looks to be some potential out there...but first there's the caveat that this is in no way an official forecast. There is a lil dash of wishcasting though. Deterministic long range guidance reflects an upper level trough dipping down into the northern/northeastern CONUS late next week. Now the northern/eastern CONUS has the greatest potential for seeing cooler temperatures behind the associated cold front, but there are quite a few members of the GEFS and Euro ensembles showing cooler than normal temperatures towards the end of next week.

Again, it's not a guarantee, but it is something that I'm sure a lot of us would like to see come to fruition. The current normal low temperature is 67 degrees...don't start meme-ing on me just yet. The last time the City of Houston was below 67 degrees was in mid May...so here's to hoping!

Batiste

AVIATION

(12Z TAF Issuance) Issued at 600 AM CDT Tue Sep 29 2026

Look for a gradual increase in southeast winds today...with some gusts to or slightly above 20kt a possibility this afternoon. VFR conditions will mostly prevail, though we wouldn't be overly surprised to see some brief/intermittent cigs ~2500ft in the mid morning hours. There's also a non-zero chance of an isolated shra or two, but chances should be low enough to exclude from the TAFs attm. 47

MARINE

Issued at 1128 PM CDT Mon Sep 28 2026

Light to occasionally moderate onshore flow and 1-3 ft seas will persist through Tuesday afternoon before winds persist closer to the 20-25 kt range late Tuesday into Wednesday. Small Craft Advisories will likely be needed during this time period due to the elevated winds and subsequently increasing seas (into the 5-8 ft range in the Gulf). Water levels during the latter half of the week will peak around or just above 3.0 ft MLLW, not enough for coastal flooding hazards but high enough 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.

Batiste

PRELIMINARY POINT TEMPS/POPS

College Station (CLL) 96 74 97 75 / 20 0 40 30 Houston (IAH) 93 78 93 79 / 20 10 40 10 Galveston (GLS) 89 83 89 83 / 20 20 40 40

HGX WATCHES/WARNINGS/ADVISORIES

TX...None. GM...Small Craft Should Exercise Caution from 4 PM CDT this afternoon through Wednesday evening for GMZ330-335-350-355-370-375.