Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 191755
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1255 PM CDT Sat Aug 19 2017

.AVIATION...
VFR again today as surface high pressure remains planted over
(south)eastern Texas. Maybe a stray shower may pass over more
coastal hubs in the next couple of hours...further inland across
the second tier counties/metro along and ahead of a lifting late
afternoon sea breeze front. Subtle backing and strengthening of
the southeast breeze in relation to this passing sea breeze
boundary. Sporadic short-lived overnight formation of MVFR
decks...mixing out to a few-sct cumulus field by late morning. 31

&&

.PREV DISCUSSION... /ISSUED 1013 AM CDT Sat Aug 19 2017/

UPDATE...
Another hot and humid day is expected for Southeast Texas with
upper ridging over the region resulting in high temperatures in
the mid 90s to near 100 inland and upper 80s to low 90s along the
coast. Afternoon heat index values will again flirt with heat
advisory criteria in the 103 to 108 range, but holding off for now
as atmospheric column over most of Southeast Texas is slightly
drier than 24 hours ago and not expecting the coverage of higher
heat index values that was observed yesterday. (However, light
winds today will still make being outside feel very hot.) The
exception to this drier column is located across the northeastern
counties where GOES-16 total precipitable water imagery shows a
plume of 1.8-2 inch PWATs across Houston, Trinity, and Polk
counties. Will have to monitor these areas (and areas generally
east of I-45 today should this plume sink farther south faster
than previous satellite trends have indicated) for a possible
short-fuse heat advisory.

Otherwise, have added a mention of isolated showers to the
coastal waters and immediate coastal areas for the remainder of
the morning based on radar trends. Also added an isolated
thunderstorm mention across the lower two tiers of counties for
activity along the sea breeze this afternoon as well as across the
northeastern counties for diurnally driven convection within the
aforementioned moisture plume.

Huffman

PREV DISCUSSION... /ISSUED 622 AM CDT Sat Aug 19 2017/

AVIATION...
Fairly light winds this morning out of the SW. Decided to carry
periodic MVFR cigs for the morning hours, potentially impacting
TAF sites including HOU/SGR and northward. With conditions today
similar to yesterday, based on forecast soundings and observations
from yesterday morning, thinking MVFR conditions mainly between
11-14Z for the northern TAF sites and an hour later for the HOU
TAF sites. Not as confident MVFR conditions will impact HOU/IAH
based on the trends seen on the GOES-16 fog channel. With daytime
heating, again thinking ceilings should mix out fairly early this
morning allowing VFR conditions to follow. Expecting a turn in the
winds late afternoon from SW to SE associated with the seabreeze,
which could also help to provide enough moisture for a stray
shower or thunderstorm. Decided to keep VCSH/VCTS out of the TAFs
for all sites, though the potential for an isolated shower/storm
is not out of the question. Forecast soundings/MOS guidance are
again lowering cigs Sunday morning so could potentially see a
persistent forecast in store again for tomorrow.

Hathaway

PREV DISCUSSION... /ISSUED 427 AM CDT Sat Aug 19 2017/

DISCUSSION...
Surface analysis shows a pretty weak pressure gradient so mainly
calm winds across SE Texas this morning. This has allowed for
temperatures to drop into the mid/upper 70s for rural areas, but
the Houston urban heat island is in full force with temperatures
still in the low 80s. And then there is Galveston holding onto the
mid 80s and heat index in the upper 90s.

Upper level analysis at 00z shows a fairly flat ridge across Texas
and the northern Gulf of Mexico. An upper level trough was moving
across the Midwest and Great Lakes. Out in the SE Gulf over the
Florida Keys, water vapor imagery depicts a broad closed off TUTT
which should continue to move west across the Gulf as forecast.

Over the weekend the heat will still be the main headline. While
heat advisory will not be issued at this time since heat index
values are expected to be around 103 to 107, there still could be
a few areas that reach above 108 and an advisory could be issued
later today for the afternoon. The same can be said for Sunday.

The coming work week may actually be more wet than dry, but that
will largely hinge upon upper level ridging or the lack there of.
The TUTT over the Florida Keys is expected to track towards the NW
Gulf by Tuesday. This is about a day slower compared to
yesterday`s forecast data so while rain chances are higher on
Monday than Tuesday, possible that the better rain chances could
be on Tuesday. Precipitable water values for the GFS go up from
1.7-1.8 inches on Monday to 1.9 on Tuesday. That said, the NAM is
the opposite with higher moisture on Monday. Still, the main idea
being that scattered showers and thunderstorms will be possible
both days. Viewing of the solar eclipse will still be in doubt for
areas around Houston, but areas from College Station to
Huntsville should still have a good view.

Next Wednesday through Saturday the TUTT over the NW Gulf should
weaken and shear out between a trough over the Great Lakes and
ridging developing over the northern Gulf. The trough does help a
front move into Texas for the end of the week but still unsure
where exactly it stalls. The Canadian and ECMWF seem to have the
front stall Friday along the coast or just offshore in the Gulf.
GFS still has the front inland but with a back door component that
could have the front stall from along I-10 at the TX/LA border
back NW towards C TX. With the front sagging south for the end of
the week, the forecast will hold onto mainly 20-30 PoPs with no
one day having any better chance than the other. Forecast going
forwards will try to pinpoint when higher rain chances will occur
with perhaps Friday being that day.

Overpeck

TROPICS...
IR Satellite imagery shows that TS Harvey has a respectable
nocturnal flare up in convection as it continues to trek WNW
across the Caribbean. There is not much change in the NHC forecast
track as landfall looks to be in Belize early Tuesday. NHC does
have the remnants of Harvey emerging in the Bay of Campeche early
Thursday, but difficult to know at what kind of intensity.
Synoptic models and ensemble guidance suggest the remnants could
organize again with a second landfall in Mexico near Tampico
towards the end of the week. This track make some sense with upper
level ridging expected to build over the northern Gulf during
this time. That said, the track forecast is highly uncertain
considering the intensity of what`s left of Harvey are unknown and
hard to know how much land interaction will weaken the system.
Best course of action remains to monitor the situation and double
check preparedness plans.

Overpeck

MARINE...
No big changes to the marine forecast this evening. Observations
still indicate light winds out of the southwest with seas between 2-
3 feet. Seas should begin to lower to 1-2 feet later in the weekend,
due to the influence of high pressure located over the northwestern
Gulf of Mexico. Dry conditions can be expected through Sunday with
precip chances on the rise Monday as a disturbance approaches from
the southeast.

Additionally, little fluctuation in the tide forecast. Tides are
running right around normal to slightly above normal by a half foot
at times.

Hathaway

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      76  99  76  98  76 /  10  10  10  10  10
Houston (IAH)              77  96  78  94  78 /  10  20  10  30  10
Galveston (GLS)            82  90  82  89  82 /  10  20  10  30  10

&&

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

$$

Discussion...14
Aviation/Marine...31



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