368
FXUS64 KHGX 300419
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1119 PM CDT Tue Sep 29 2026

...New DISCUSSION, AVIATION, MARINE...

.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.

-------------

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!

-------------

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.

-----------

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...
(06Z TAF Issuance)
Issued at 1119 PM CDT Tue Sep 29 2026

This evening and overnight, VFR conditions prevail. Winds currently
out of the SE around 10 kts will gradually lower to the 6-8 kt range
overnight. Early tomorrow morning, there is a chance for MVFR CIGs
around FL020 - 030. This MVFR cloud decks creeps in from the
northwest. The best chance for MVFR criteria being met will be at
the northern TAF sites. Tomorrow afternoon, winds remain out of the
SE but pick back up to the 10-15kt range with gusts up to 25 kt
possible. As for precipitation, showers and storms look to be
isolated- scattered in nature. Showers may start as early as 11Z
along the coast, and traverse inland throughout the day tomorrow.
Any showers/storms that develop may be capable of producing heavy
rain, which can lower visibility. Winds are expected to drop off
their gusts by tomorrow evening, but remain around 10 kts out of
the SE.

MLG

&&

.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)  75  95  75  93 /   0  30  10  80
Houston (IAH)  78  93  79  92 /  10  50  10  70
Galveston (GLS)  83  89  83  89 /  20  30  10  60

&&

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

&&

$$

DISCUSSION...Batiste
AVIATION...MLG
MARINE...Batiste