Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 211609
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1109 AM CDT Mon Aug 21 2017

.UPDATE...
Drier air moving into the region from the Gulf this morning and
this is likely what is keeping the radar mainly quiet. The upper
low over the Gulf is forecast to continue its slow westward trek
towards the local waters through early tomorrow. Shower and
thunderstorm coverage should increase over the coming hours...if
not from lift along this low`s far western reaches...along the
sea breeze boundary. Decent cumulus field quickly sprouted up in
the last hour so anticipating that many may find it challenging
to find a nice...clear view of this afternoon`s partial solar
eclipse. Optimal viewing of the eclipse is in a couple of
hours...or around 1:15 PM CDT. 31

&&

.PREV DISCUSSION... /ISSUED 623 AM CDT Mon Aug 21 2017/

AVIATION...
VFR conditions across a majority of SE TX this morning, with the
possibility of MVFR ceilings moving in during the morning hours for
CLL, UTS, and CXO. Radar imagery shows showers working their way
onshore this morning, but not within the vicinity of LBX or GLS
as of yet. Coverage should change from isolated to more widely
scattered with the help of daytime heating, and shr/ts should move
further inland later in the afternoon. Not expecting convection
to reach too far north, as drier air and subsidence could prevent
development from reaching UTS and CLL. Therefore, kept VCTS for
all TAF sites CXO and southward, but think the coastal and Houston
TAF sites will see the best chance for activity. Should see a
clearing trend behind the main band of development along the
sea/bay breezes so have the coastal TAF sites clearing around
22-23Z and the Houston TAF sites a little later between 01-02Z or
near sunset. Some high clouds should linger through the overnight
hours, with clearer skies to the north for CLL and UTS.

Hathaway

PREV DISCUSSION... /ISSUED 352 AM CDT Mon Aug 21 2017/

DISCUSSION...
So the real question is not whether you can see the eclipse from
your backyard but whether it will rain in your back yard. Most of
SE Texas is running good 1 inch of rainfall below normal for the
past 7 days. And below normal precipitation has been the trend for
even the last 30 days except for a corridor from Austin, Waller,
Harris, Liberty counties that has seen rainfall 3 to 5 inches
above normal. As far as today goes, it looks like a good 30 to 40
percent chance of rain for areas around Houston southward to the
coast. The tropical upper tropospheric trough continues to spin
over the central Gulf and this feature should move closer to the
NW Gulf by tonight and Tuesday. GOES 16 derived PW imagery does
show a plume of 1.8 to 2 inch precip water over much of the area
and east Texas. So with lowering heights and increased moisture,
there should be widely scattered showers and a few thunderstorms
beginning in the late morning continuing through the afternoon.
Scattered activity will afford a few breaks in the clouds so most
of the area should still be able to view the eclipse, just know
that it may disappear behind some clouds from time to time.

Tonight into Tuesday both the NAM/GFS indicate a drop in
precipitable water over the region which may limit rain chances to
just along the coast with 20 to 30 percent chances. The TUTT will
still be in play over the NW Gulf and should keep lower heights
in place but PW of 1.5 to 1.7 may not be enough to support
scattered showers and storms. By Wednesday the TUTT seems to shear
out a bit and weaken over the W Gulf. But GFS does show PW
increasing closer to 2 inches by Wednesday and the suite of
NAM/GFS/ECMWF/Canadian all indicate a frontal boundary pushing
into Texas from the north. Some show the front reaching a Waco to
Shreveport line by Wednesday evening. Convergence near the
surface with the front and moisture from the south along with
lower heights aloft still support at least a 30 percent chance for
Wednesday.

Thursday through the weekend rain chances will hinge on a couple
of factors. 1. How far south the front pushes before stalling
Thursday/Friday. 2. Surge of moisture if the remains of Harvey can
organize again in the southern Gulf/Bay of Campeche. As far as #1
goes, the NAM/ECMWF both push the front to around I-10 on
Thursday. GFS is a touch farther north with its position and the
Canadian close that which it had been pushing the front into the
Gulf. For #2, well all bets are off since remnants of Harvey are
still poorly organized and are about to push across much of
Yucatan tonight into Tuesday. It should emerge in the Bay of
Campeche Tuesday night or Wednesday. From there all the synoptic
models like some type of development as it tracks NW reaching the
Mexican coast Friday morning. So there may be higher tropical
moisture moving into SE Texas for the weekend but largely depends
on if Harvey can organize again and its track. For now the
forecast will keep rain chances conservative in the 30 to 40
percent range until more is known about the remnants of Harvey.

Overpeck

TROPICS...
This morning GOES 16 IR shows the remnants of Harvey stretching
from north to northeast of Honduras as it moves into the NW
Caribbean Sea. Convection is poorly organized and the open
tropical wave should move across Yucatan and emerge into the Bay
of Campeche late Tuesday night into Wednesday. Ridging at 850mb
and 300mb do increase for the end of the week and should provide
steering of any system towards the Mexico coast. Ridging at 500mb
is not quite as strong or established but enough along the
northern Gulf to aid in overall steering of the system. Reality is
that if the tropical wave cannot organize into a cyclone again
before the Yucatan, it very well could get ripped apart by its
interaction with land. This is still very much a wait and see
situation.

Overpeck

MARINE...
Little change in the marine forecast this evening. Currently,
seas are at 2 feet and are expected to raise to 2-3 feet by mid
week. South to southeasterly winds should prevail through much of
the week, remaining light between 5-10 knots. For Monday morning,
should begin to see development mainly over the western waters
expanding eastward by early morning with the help of the
seabreeze, eventually moving onshore by late morning. Therefore,
expecting isolated to widely scattered coverage over the waters.

Tides tonight are again around normal and should stay at normal to
slightly above normal by less than a half foot, through much of the
week.

Hathaway

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      98  75  98  75  99 /  20  10  20  10  30
Houston (IAH)              94  77  95  77  96 /  40  10  20  10  30
Galveston (GLS)            93  83  91  82  91 /  30  10  30  10  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...31



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