901
FXUS64 KHGX 171135
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
635 AM CDT Mon Jun 17 2024

...New AVIATION...

.SYNOPSIS...
Issued at 254 AM CDT Mon Jun 17 2024

A broad area of low pressure is expected to materialize in the
southwestern Gulf of Mexico today or tonight. The system will push
deep tropical moisture into southeast Texas over the next few
days. Conditions are conducive for gradual development into a
tropical depression or tropical storm by mid-week. However, the
overall impacts are likely to be the same regardless of
development.

Key Points

1) There is a daily risk of heavy rainfall beginning today and
   lasting through Thursday.

2) The best chance of heavy rainfall capable of flooding is late
   Tuesday into Wednesday.

3) Hazardous winds and seas are likely offshore and in the bays
   through much of the upcoming week.

4) Coastal flooding is possible Tuesday night into Wednesday, and
   possibly Thursday, along the Upper Texas Coast.

&&

.SHORT TERM...
(Today through Wednesday) Issued at 254 AM CDT Mon Jun 17 2024

TODAY

As of writing this AFD, spotty showers and thunderstorms over the
Gulf are already pushing towards the coast, a sign that our surge
of deep tropical moisture has begun. PWATs are already 1.50-1.80"
and rising. HREF ensemble mean PWATs show values surpassing 2.00"
for most areas east of I-45 and south of I-10 by this afternoon.
Such high PWATs are indicative of an environment favorable for
heavy rainfall. Most of the southern half of the CWA remains in a
Slight Risk (Level 2 of 4) for excessive rainfall today, while
areas farther north are in a Marginal Risk (Level 1 of 4).
Widespread totals are expected to be manageable today. But
locally heavy downpours capable of dropping a quick 2-4 inches of
rain cannot be ruled out. Shower and thunderstorm activity is
expected to diminish overnight. However, rain and thunderstorm
chances will remain elevated over the Gulf. Winds will increase
through the day (especially at the coast) thanks to the steepening
gradient between the Gulf low and an area of high pressure over
eastern CONUS. By this afternoon, winds at the coast could be
gusting near 30 MPH.

TUESDAY-WEDNESDAY

Deep tropically oriented LL flow will push PWAT values even higher
on Tuesday. Global and HREF ensemble means suggest a very high
chance of widespread peak PWATs of at least 2.25-2.50 inches
Tuesday evening through Wednesday afternoon. Ensemble PWAT means
near the coast are closer to 2.75 inches while deterministic
guidance suggests the possibility of 3.00 inch PWATs near the
coast. By Tuesday afternoon, the Gulf low (whether a tropical
system or not) may already be producing rainbands on the north and
east side of the circulation. With deep moisture in place, these
rainbands and their embedded thunderstorms will be primed to
produce heavy rainfall. Though scattered showers/thunderstorms and
locally heavy rain are a concern Tuesday afternoon, it is really
Tuesday evening into Wednesday where the best chance of heavy
rainfall occurs.

Most of the southern half of the CWA (including the City of
Houston) is under a Moderate Risk (Level 3 of 4) for excessive
rainfall Tuesday evening through Wednesday. The northern half of
the CWA is in a Slight Risk (Level 2 of 4). Though there is
general consensus that rainfall totals will be higher near the
coast, uncertainty remains regarding the location of the heaviest
rainfall due to continued forecast complexities. For example,
rainfall could become enhanced by small vorticity maxima embedded
in the LL flow. Overnight global deterministic runs suggest that
these vort maxes are more likely to track into the central Texas
Coast, suggesting that the heaviest totals could occur south of
our region. However, ensemble data is quick to point out that
southeast Texas remains in the risk zone for these corridors of
higher rainfall totals. Current predicted storm total (Monday-
Thursday) rainfall ranges from 6-10 inches near the coast, to 4-6
inches along the I-10 corridor, and 2-4 inches over most of our
northern counties.

Heavy rainfall will not be the only concern. Strong coastal winds
are likely Tuesday and Wednesday. Winds at the coast could gust
over 40 MPH. These winds will result in hazardous seas, rough
surf, and dangerous rip currents. We have also issued a Coastal
Flood Watch for tonight through Wednesday night due to the
prospect of water levels 4-5 feet (potentially up to 6 feet) above
Mean Lower Low Water (MLLW) during high tide. In addition to the
high coastal winds, models suggest a LLJ in the 925-850MB layer
where winds could be 40-50 knots in the jet`s core. Any embedded
thunderstorm would have the opportunity to mix these winds down to
the surface. Generally speaking, the severe weather threat is
considered low. However, isolated damaging wind gusts cannot be
ruled out, especially near the coast.

.LONG TERM...
(Thursday through Sunday) Issued at 254 AM CDT Mon Jun 17 2024

Unfortunately for those sick of the rain, the pattern appears to
remain unsettle through week`s end. Residual moisture from the
current system may still be with us on Thursday, bringing a chance
of locally heavy showers and thunderstorms. Increased mid/upper
ridging may attempt to bring drier conditions to the CWA on Friday
and Saturday. Fri-Sat PoPs are much lower across our northern
counties. However, we opted to keep 30-50 PoPs across the southern
CWA since the global models don`t think the ridging will be
sufficient to eliminate shower/thunderstorm activity.

&&

.LONG TERM...
(Thursday through Sunday) Issued at 254 AM CDT Mon Jun 17 2024

Unfortunately for those sick of the rain, the pattern appears to
remain unsettle through week`s end. Residual moisture from the
current system may still be with us on Thursday, bringing a chance
of locally heavy showers and thunderstorms. Increased mid/upper
ridging may attempt to bring drier conditions to the CWA on Friday
and Saturday. Fri-Sat PoPs are much lower across our northern
counties. However, we opted to keep 30-50 PoPs across the southern
CWA since the global models don`t think the ridging will be
sufficient to eliminate shower/thunderstorm activity.

&&

.AVIATION...
(12Z TAF Issuance)
Issued at 635 AM CDT Mon Jun 17 2024

Forecast ahead is challenging to say the least, and though I`d
love a perfect TAF, I suspect amendments lie in the future.
Broadly speaking, however, confidence is fairly high in an
increasingly rainy pattern as a tropical airmass moves in,
associated with area being monitored in the southern Gulf/Bay of
Campeche. Should be mostly showers, but can`t rule out thunder
this afternoon, so have some TEMPOs for that possibility. Coverage
of showers is isolated to scattered this morning, and should
become more numerous to widespread with time. CIG/VSBY generally
VFR, but could see VSBY restrictions in heavier rain, and some
MVFR CIGs later tonight as tropical moisture surges in.

&&

.MARINE...
Issued at 254 AM CDT Mon Jun 17 2024

A broad area of low pressure over the southwestern Gulf of
Mexico will bring unsettled weather to the Gulf waters through
much of this week. Look for increasing winds, seas, and water
levels across the upper Texas coastal waters over the next few
days. Small Craft Advisory conditions are expected to begin today
and last through much of the week. The chance of gale force winds,
at least in gusts, is increasing for the Tuesday to Wednesday time
frame. Seas offshore are expected to easily exceed 10 feet and
could potentially approach 15 feet. Mariners should closely
monitor the forecasts.

&&

.HYDROLOGY...
Issued at 408 PM CDT Sun Jun 16 2024

Ongoing river flooding persists for a few sites along the Trinity
River. The Trinity River near Liberty continues to gradually rise in
moderate flood stage and may crest into major flood stage later this
week. The Trinity River at Riverside crested in moderate flood
stage, but will take a while to recede. The Trinity River at Moss
Bluff continues on a slow and gradual climb in minor flood stage.
The current forecasts do not take into account the upcoming rainfall
event later this week.

We are continuing to monitor an area of disturbed weather currently
over the Yucatan Peninsula that is expected to become a broad
surface low in the Bay of Campeche (southwestern Gulf of Mexico)
over the next few days. This low would then have the potential to
become a tropical depression by midweek as it moves slowly westward
or west-northwestward. REGARDLESS OF TROPICAL DEVELOPMENT, the
deeper tropical moisture from this system will bring periods of
moderate to heavy rainfall for portions of Southeast Texas (mainly
areas near and south of I-10). Tuesday into Wednesday in particular
look to be the main days with heavy rainfall potential. Locally
heavy rainfall may lead to localized instances of street flooding in
some areas. Forecast uncertainty remains rather high though, but for
now we`re continuing with the messaging of 5-8" of rainfall near and
south of US-59/I-69 and 2-4" north of US-59/I-69. That total
rainfall forecast is over a four day period from Monday-Thursday.
New river flooding will be possible as early as Tuesday. We`ll also
be monitoring for the potential for flooding along area creeks and
bayous as well. With there being general consensus for the higher
end of the rainfall amounts occuring near/along the coast, this will
be beneficial rainfall for drought stricken areas (mainly those near
Matagorda Bay).

Remember to heed any instructions from your local officials and to
never travel through ANY flooded areas or roadways. TURN AROUND,
DON`T DROWN. Please monitor updated forecasts via the NWS NWPS
webpage (https://water.noaa.gov/).

Batiste

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)  91  75  89  74 /  50  10  30  30
Houston (IAH)  89  76  85  74 /  70  30  70  70
Galveston (GLS)  87  80  85  78 /  80  50  80  80

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Coastal Flood Watch from late tonight through late Wednesday
     night for TXZ214-313-335>338-436>439.

     High Rip Current Risk from 10 AM CDT this morning through
     Tuesday morning for TXZ436>439.

GM...Small Craft Should Exercise Caution until 1 PM CDT this
     afternoon for GMZ330-335-350-355-370-375.

     Small Craft Advisory from 1 PM this afternoon to 7 AM CDT
     Thursday for GMZ330-335-350-355-370-375.

&&

$$

SHORT TERM...Self
LONG TERM....Self
AVIATION...Luchs
MARINE...Self