Flash Flood Warning 24, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
619 AM CDT Sat Jun 20 2026

...New AVIATION...

.KEY MESSAGES...

- Elevated heat stress remains possible this weekend outside of
  areas with clouds and rain. A Heat Advisory remains in effect
  for the greater Houston area today.

- Periods of scattered to numerous showers and thunderstorms will
  persist through Sunday morning, with the potential for locally
  heavy rainfall today. There is a level 2 out of 4 risk for
  excessive rainfall through the daytime hours today, mainly north
  of I-10.

- A high risk of strong rip currents will continue over the
  weekend.

&&

.DISCUSSION...
Issued at 1223 AM CDT Sat Jun 20 2026

After scattered storms yesterday afternoon, only light shower
activity remains across our area early this morning, mainly along
the coast. However, ongoing elevated convection across central
and south TX may spread into southeast TX through the early
morning hours as persisting low level flow results in increasing
isentropic ascent. While guidance is still not fully on the same
page with regards to the evolution of these storms through today,
there is general consensus in the morning convection being more
focused across our interior areas from Houston to the north and
west, with activity shifting southward toward the coast through
the daytime. Any areas that see greater coverage during the early
portion of the day will likely see minimal or lesser activity this
afternoon. And similarly, areas that avoid substantial rain in
the morning will have a greater chance this afternoon. While most
areas will receive less than an inch of rain with today's
showers and storms, the moist airmass will be supportive of
locally higher rainfall amounts that may result in localized
flooding. WPC is maintaining a marginal to slight risk for
excessive rainfall, with highest probs generally north of I-10
and east of I-45. Conditions appear less favorable for isolated
severe storms today, but lightning could still be an issue at
times.

It now appears increasingly probable that ongoing convection and the
resulting cloud shield today will limit temperatures enough to
prevent heat indices from being as extreme as in recent days. Given
this, we will pare down the Heat Advisory to focus mainly on the
greater Houston area. Still, triple digit (38C+) heat indices are
possible within a very muggy airmass characterized by dewpoints in
the upper 70s to around 80F (25-27C). And with many outdoor
festivities planned this weekend, we want to continue to urge
appropriate caution for anyone spending time outdoors.

Looking ahead to the overnight hours tonight through early Sunday
morning, latest guidance suggests we may see a repeat of the
nocturnal elevated convective development we're seeing this early
morning but instead initiating further south along the coast and
over the coastal waters, potentially spreading inland. There is
potential for this activity to fester into Sunday morning, and if
this trend holds, PoPs may need to be bumped up further for late
tonight and Sunday especially between I-10 and the coastal waters.

Beyond the weekend, rain chances will trend down again as mid level
ridging restrengthens along the northwestern Gulf coast. High temps
will trend back up toward the mid 90s (34-36C) and heat indices in
the triple digits (38C+) will remain possible. Additional heat
products cannot be ruled out next week.

&&

.AVIATION...
(12Z TAF Issuance)
Issued at 614 AM CDT Sat Jun 20 2026

Multiple rounds of showers/storms will be possible throughout
today. First round is already moving through portions of SE Texas
early this morning. Lingering showers trail behind it heading
into the early afternoon, with another uptick in showers/storm
activity possible throughout the afternoon. Showers/storms taper
off again into the evening with a lull overnight, allowing MVFR
CIGS to fill in. Another round of showers/storms could occur early
Sunday morning.

03

&&

.MARINE...
Issued at 1223 AM CDT Sat Jun 20 2026

Isolated to scattered showers and thunderstorms will be possible
through Sunday morning. Otherwise, light to moderate onshore flow
will persist through this weekend into early next week with seas
between 3 to 6 feet.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)	  89  77  92  79 /  70  20  10   0
Houston (IAH)			  90  79  93  80 /  60  20  20   0
Galveston (GLS)			  88  83  89  84 /  40  30  20   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 10 PM CDT this evening for TXZ199-200-
     212>214-227-237-238-300-313-337-338-437>439.

     High Rip Current Risk through this evening for TXZ436>439.

GM...None.
&&

DISCUSSION...DL
AVIATION...03
MARINE...DL

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