textproduct: Houston/Galveston

KEY MESSAGES

-Hot and humid conditions will continue through Wednesday.

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

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

DISCUSSION

Issued at 204 PM CDT Tue Sep 29 2026

I think my colleague had a good idea with breaking this forecast up into short-term, long-term, and longer-term periods, so in order to keep the details of this forecast more organized and not get lost in the weeds, we will continue with that set up.

So, let's start with the short-term forecast period...

We are already seeing the result of persistent onshore flow in the lower levels this afternoon as showers continue to move into the Coastal Plains from the Gulf. Looking at satellite derived PWAT values we can see a wedge of 1.8" where those showers are developing and moving inland. A closer look at the 850 mb shows decent moisture convergence in that area; however, mid-upper levels are on the drier side (that will change in the coming days) and we still remain under the influence of a ridge (ridge axis is bisecting the area)...all that to say, should primarily see shallow showers through the rest of the day. The afternoon sea breeze may be able to generate an isolated thunderstorm or two, but the favorable dynamics for that are very limited (decent capping, marginally unstable lifted index).

As we get into the overnight hours tonight into Wednesday morning, that ridge will continue to shift east, and we will see an increase in cloud cover over much of the area with the eastern periphery of our widely discussed trough approaching the area. By this point the remnants of Hurricane Polo (whose landfall into Mexico is imminent) are expected to merge into the overall flow of the the mid-upper level trough. Withe the trough approaching and the ridge exiting, the resultant tightening pressure gradient may lead to gusty winds (around 20-25 mph) at times this afternoon through Wednesday.

Wednesday is still anticipated to be more of a transition day weather wise. The positioning of southeast Texas on the eastern edge of the trough will provide the area access to mid-upper level moisture brought in from the Pacific, and we will see this moisture gradually increase through the day(GFS soundings show a slow transition to a deeper saturated profile Wednesday into Thursday and PWAT values approach 2" ). Additionally, models continue to show a surface trough developing over West Texas, stretching SEward into Mexico, and with its proximity to the surface high pressure stretching across the SE CONUS, expect to see the pressure gradient tighten across coastal areas. Conditions are bordering the criteria for a Wind Advisory across the Barrier Islands (sustained winds of 25 mph or greater), so will hold off on any advisories for this forecast package.

Otherwise, we can expect similar conditions to today for Wednesday...temperatures reaching into the 90s, heat indices getting into the triple digits for much of the area, and continued showers streaming in from the Gulf.

Alright...insert intermission and coffee break to process all of that information here..

Now lets get into the meat of the forecast...Wednesday night through the weekend

By Wednesday night models are in pretty good agreement with the position of this mid-upper low being centered over the Texas/Oklahoma Panhandles. PWAT values across our area will range from 2.0-2.4" (feel like a broken record here, but this value is well above the 90th percentile for our area). Models continue to show the potential for a few embedded shortwaves and associated vort maxes moving overhead late Wednesday into Thursday, and these could generate a few showers over the Brazos Valley/Piney Woods. The environment looks a little more unfavorable for any convection, so expect this to be primarily showers.

Closer to the coast it looks like we may have decent moisture convergence in the lower levels, so wouldn't be surprised to see a few showers along the coast overnight Wednesday into Thursday morning (honestly kind of similar to how the radar has looked through the day today).

During the day Thursday models continue to show some disagreement with the positioning of this trough. The GFS has the center of the mid-upper level low lifting into Kansas, with a secondary area of low pressure developing over eastern New Mexico. ECMWF has a slower progression (as has been the case for the last few days), with the center of the low showing a slight eastward progression into the eastern part of the TX/OK Panhandles. In both cases, we see a slow moving frontal boundary associated with the parent low, and this is expected to generate widespread showers from the Brush Country of South Texas, through the Hill Country, and NE into the DFW area. Most of the rainfall Thursday is expected to occur just outside of our CWA...models have been consistently showing that the last few days, but with the amount of moisture overhead, and embedded shortwaves and vort maxes continuing to move across the area ahead of the boundary, our CWA isn't entirely out of the woods with the flood potential...additionally, there is some concern with the models continuing to disagree on where the frontal boundary stalls...If the front pushes any further eastward and stalls, interests in the Brazos Valley would be more likely to see the impacts.

We continue to expect the heaviest rainfall for our area to occur Thursday night into Friday, and this is also where the forecast gets a little tricky...particularly with the disagreement among models...so going to try to break it down a bit.

By this point in the forecast period, our overhead environment is primed for heavy rainfall. We have DEEP tropical moisture, NBM probabilities for PWAT values greater than 2.0" range from 60% to 100% from east to west respectively...Ensembles are showing the same picture with NAEFS and ECMWF ensembles both showing PWAT values at max levels during the Thursday night into Friday timeframe.

My concern lies with the 12Z run of the GFS (not to put all of the eggs in one basket...but in this environment, certainly not something to discount either). The 500mb level shows a second area of low pressure forming as the parent trough lifts NE. This new low becomes centered over west Texas with several embedded impulses moving overhead in a closer proximity to the Brazos Valley, and a stationary front draped across Central Texas. This scenario could result in showers with heavy rain rates(3-4"/hr) across the Brazos Valley as strong moisture convergence occurs out ahead of the stationary front. This would be the area to keep an eye on over the next day/day and a half (hi-res guidance window ends just before this period).

WPC currently has all of southeast Texas in a marginal to slight risk for excessive rainfall Thursday into Friday morning. I do want to point out that the Brazos Valley is just outside of the axis of heaviest rainfall (and WPC's moderate risk area), so any deviation to the east could result in an upgrade to the excessive rainfall outlook...it could also trigger a Flood Watch for that area (holding off on that for now).

WPC maintains a Marginal Risk for the entire area through the majority of the weekend, so will need to continue to monitor the flood potential through this time. In any case, it is important to continue to monitor the forecast as we approach this event.

With the previous paragraph, it's relevant to say that rain is expected to continue through the weekend as elevated moisture persists. Current QPF for the area through the weekend sits around 2-4" with the higher totals further north and west (coastal areas could see some 3" totals with the influx of Gulf moisture). Again, with the uncertainty in the forecast, don't get too fixated on the current QPF...it is still subject to change and could increase as we get closer to the event.

A brief nod to temperatures...they'll be more seasonal later in the week and into the weekend (thanks rain and clouds).

Bailey

AVIATION

(18Z TAF Issuance) Issued at 1236 PM CDT Tue Sep 29 2026

Isol showers west of I-45 continue to move inland and may increase in coverage as the sea breeze. The SE breeze will continue to increase over the afternoon with gusts up to 20kts across all terminals. Tonight, winds prevail out of the SE between 5-10kts. CIGs begin to fill in during the morning hours as tropical moisture arrives creating the potential for MVFR CIGs and becoming the main flight category impact. With the arrival of moisture, PROB30 for showers are becoming more confident. At this time TS has been left out due to lower probabilities and confidence on terminal impacts. Coverage and timing will continue to be monitored going forward.

CMW

MARINE

Issued at 204 PM CDT Tue Sep 29 2026

Light to occasionally moderate onshore flow and 1-3 ft seas will persist through this 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/Bailey

PRELIMINARY POINT TEMPS/POPS

College Station (CLL) 74 95 76 93 / 0 40 30 90 Houston (IAH) 78 92 79 92 / 20 40 30 60 Galveston (GLS) 83 89 83 89 / 20 40 30 50

HGX WATCHES/WARNINGS/ADVISORIES

TX...None. GM...Small Craft Should Exercise Caution through Wednesday evening for GMZ330-335-350-355-370-375.