Flash Flood Warning 28, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
623 AM CDT Fri Jul 9 2021

.AVIATION [12Z TAF Issuance]...

Another day of widespread showers is expected today with scattered
thunderstorms developing in the late morning and afternoon. MVFR
CIGs of 2000-3000ft will prevail, but expect lower CIGs and
visibility during times of rain. Southeasterly flow will persist
through the package. Coverage of precipitation will end from south
to north late this afternoon into the evening with all the
terminals seeing an end to the precipitation by 00 to 03z. The
MVFR cigs of 1500-2500ft will continue through the night. Drier
conditions are expected on Saturday with much less precipitation
coverage.

Fowler

&&

.PREV DISCUSSION /Issued 500 AM CDT Fri Jul 9 2021/...

.SHORT TERM [Through Saturday Night]...

A very welcome reprieve from the heavy rain occurred during the late
evening through 2am. Though, radar is filling in across the Gulf and
this will be moving inland within the next few hours. Guidance
didn't pick up this break in the rainfall, so did cut back some of
the QPF expected through the morning. The break allowed for some
decrease in the swollen rivers along the Lavaca/Navidad in
preparation for the return of the heavy rain - which will occur by
sunrise. A strengthening LLJ will be oriented south/north extending
from the waters off of Corpus and up through the western half of the
area. This axis is where the heaviest rains will fall this morning
and into the early afternoon. The showers and thunderstorms should
be able to push a bit further inland today with precipitation
reaching up through around the Lake Livingston area. PWATs today
will be around 2.1 to 2.2 inches, so locally heavy rainfall will be
possible within any of these storms. However, these northern areas
have not received as much rain as the coastal areas over the past
few days, so will be able to take the excess rainfall better.
Through this evening, expecting an additions 3 to 6 inches of rain
south of I-10 and west of the Brazos River with areas to the north
and east expecting up to 1 to 3 inches. Locally higher amounts are
possible. There is hope for drier conditions starting tonight. The
upper level low begins to move southwestward into northern Mexico
tonight and high pressure to the north builds southwards pushing the
weak boundary thats been over the region out into the Gulf. This
will decrease precipitation chances on Saturday (cannot out rule
some afternoon showers and thunderstorms near the coast) with
minimal chances after sunset Saturday.

The Flash Flood Watch continues through this evening for areas
across the southwest and up along the coast. The Watch was expanded
northwards last evening to include Waller, Colorado, and Austin.
Paying close attention to Jackson, Matagorda, and Wharton counties
as these areas have one hour FFG between 1 and 2 inches with some
portions of Jackson and Matagorda even below 1 inch. So it won't
take much to cause issues. Elsewhere, the one hour FFG is between 2
and 4 inches, so while not as low, low enough to have to monitor for
any training or intense storms.

Mostly cloudy skies will continue the cooler than normal afternoon
temperatures today with highs in the low to mid 80s. However,
temperatures begin to climb on Saturday due to breaks in the cloud
cover with afternoon highs climbing to near 90. Overnight lows
tonight and Saturday night will be in the mid to upper 70s.

Fowler

.LONG TERM [Sunday Through Friday]...
Sunday morning the pesky rain producing upper low will be shunted
well south in western/southwestern Mexico with a sliver of ridging
over TX as an upper low drops out of the High Plains and into
Missouri leaving SETX in the gap with light northerly flow aloft
and still somewhat moist lower level flow off the Gulf. Rain
chances will continue Sunday with coastal showers in the morning
then some widely scattered showers and thunderstorms inland during
the afternoon. Warmer as well with highs reaching the upper 80s
near the coast and around 90 to lower 90s inland. The cold front
associated with the upper low in MO drops south and slows/probably
stalling just north of the CWA but will need to watch for the
possibility that outflow sags off the boundary and storms creep
southward Sunday night and Monday so will continue to the forecast
for higher rain chances across the northeastern counties Sunday
night and into Monday. Tuesday the upper low lifts out and the strong
Atlantic ridging pushes into the SE US and eventually into the
Gulf Wednesday. This is going to bring a wave of deeper tropical
moisture out of the Gulf and into TX with an increase in rain
chances Tuesday and Wednesday following the typical summer
diurnal pattern with the seabreeze inland. Warmer temperatures
also possible if doesn't get too cloudy from the showers and
thunderstorms. For now have stuck with highs in the lower 90s but
these may need a nudge up especially in the west and northwest.

The upper ridge over the Gulf/SE US weakens Thursday and Friday
with enough moisture lingering over SETX for scattered showers and
thunderstorms mainly driven by the seabreeze. Looking at next
Friday into the weekend upper ridging rebuilds over the 4 corners
and SETX hangs out on the edge so more of the typical diurnal
seabreeze showers/thunderstorms in the offing.
45

.MARINE...
Moderate to strong onshore flow will continue today gradually
relaxing this afternoon and tonight. SCA will be gradually coming
down to SCEC this afternoon and tonight with the stronger winds
and higher seas over the western waters. Scattered to
numerous/frequent showers this morning then tapering down in
coverage. As the low moves west winds should be very gradually
relaxing and returning to the more typical summer 10-15kt flow.
Elevated tide levels will continue today and Saturday then slowly
diminish as well while rip currents remain strong probably through
Saturday. Surge of deep tropical moisture moves into the coastal
waters area Monday or Tuesday and could see an uptick in
showers/thunderstorms with this arrival.

.HYDROLOGY...
Swelling rivers/streams and bayous over the southern CWA
especially focusing on the Lavaca Navidad/Tres Palacios/Mustang
Colorado/San Bernard. Moderate flooding ongoing near Midfield on
the Tres Palacios with more rainfall coming and further rises
likely may reach into major if all the rain materializes.

.TROPICAL...
Elsa near Long Island NY moving back out into the Atlantic.
Elsewhere the tropics look quiet - also of note quite the dust
storm brewing over Africa this morning.
45

.CLIMATE...
Intercontinental tied the 1906 record low maximum temperature
yesterday of 81 degrees.

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  84  75  90  75  90 /  70  20  20   0  20
Houston (IAH)          82  76  90  76  91 /  80  30  30   0  20
Galveston (GLS)        87  81  89  80  87 /  70  50  30  10  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...High Rip Current Risk through late tonight for the following
     zones: Bolivar Peninsula...Brazoria Islands...Galveston
     Island...Matagorda Islands.

     Flash Flood Watch through this evening for the following zones:
     Austin...Bolivar Peninsula...Brazoria Islands...Coastal
     Brazoria...Coastal Galveston...Coastal Jackson...Coastal
     Matagorda...Colorado...Fort Bend...Galveston
     Island...Inland Brazoria...Inland Galveston...Inland
     Jackson...Inland Matagorda...Matagorda
     Islands...Waller...Wharton.

GM...Small Craft Advisory until 1 PM CDT this afternoon for the
     following zones: Coastal waters from High Island to
     Freeport TX out 20 NM...Galveston Bay...Matagorda
     Bay...Waters from High Island to Freeport TX from 20 to 60
     NM.

     SMALL CRAFT SHOULD EXERCISE CAUTION from 1 PM CDT this afternoon
     through this evening for the following zones: Matagorda Bay.

     SMALL CRAFT SHOULD EXERCISE CAUTION from 1 PM to 5 PM CDT this
     afternoon for the following zones: Coastal waters from High
     Island to Freeport TX out 20 NM...Galveston Bay...Waters
     from High Island to Freeport TX from 20 to 60 NM.

     Small Craft Advisory until 7 PM CDT this evening for the
     following zones: Coastal waters from Freeport to Matagorda
     Ship Channel TX out 20 NM...Waters from Freeport to
     Matagorda Ship Channel TX from 20 to 60 NM.

&&