Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 171739
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1239 PM CDT Thu Aug 17 2017

.AVIATION...
VFR this afternoon except N of UTS where SHRA/TSRA continue to gradually
build southward toward the site. Will continue to monitor progress
of this activity and amend UTS when needed.  42
&&

.PREV DISCUSSION... /ISSUED 954 AM CDT Thu Aug 17 2017/

UPDATE...
A heat advisory is in effect for the entire CWA through 7 PM this
evening. High temperatures in low 90s right along the coast to
near 100 across the Brazos Valley coupled with high humidity will
cause heat indices to rise into the 106-110 degree range this
afternoon. In addition to the afternoon heat, Galveston is on
pace to once again set a record high minimum temperature for
today. Houston Hobby and Galveston both tied their monthly record
for record high minimum temperatures yesterday, indicating that
there has been little to no relief from the heat even during the
overnight hours.

Otherwise, a complex of thunderstorms currently over FWD`s area
should continue to drift southeastward through the day today,
likely clipping portions of the Piney Woods region. This complex
has been fairly slow-moving so far, so some locally heavy rainfall
could be possible. However, no significant impacts are expected.
Across the rest of the area, some streamer showers are possible
this morning with perhaps a thunderstorm or two mixed in this
afternoon.   11

PREV DISCUSSION... /ISSUED 419 AM CDT Thu Aug 17 2017/

DISCUSSION...
A fairly complex pattern was in place over Southeast Texas early
this morning. An upper level low pressure trough at 200-300 mb
extended into the forecast area from the southern Gulf of Mexico.
A shear axis was in place over the western part of the upper
trough, mainly across the northern and central parts of the state.
This axis was co-located with a moisture axis where PWs
approached 2.4 inches. A secondary moisture axis was over
Southeast Texas where PWs approached 2 inches. Finally, an upper
level high pressure ridge extended across the northern Gulf of
Mexico to over the forecast area.

The main items of concern today include high heat index values and
chances for showers and thunderstorms. With the axis of higher
moisture just to the north and northwest, and with the secondary
axis overhead, dewpoints may stay high enough this afternoon for
the heat index to approach advisory levels (108 degrees). However,
model blends showed the potential for enough mixing for the heat
index to be a bit lower--mainly between 205 and 207 with an
isolated area of 108-109 here and there. It will be close, but am
not confident enough to issue an advisory at this time. Best
chances for showers and thunderstorms will be over the eastern
and northern counties. Isolated showers will be possible mainly
over the coastal counties and off the coast through mid morning.
May see the seabreeze get active later this morning and this
afternoon. Any storms that do develop will help alleviate the heat
at least temporarily. Enough moisture will remain overhead for
best rain chances over the eastern and northern areas once again
on Friday.

The models then show that the subtropical ridge aloft should build
over Southeast Texas; although, an approaching upper level trough
from over the Gulf of Mexico will help weaken the ridge on Sunday.
This should lead to diminished rain chances on Saturday and
Sunday. The upper level trough will then bring slightly cooler
temperatures and increase rain chances on Monday. The GFS and
ECMWF differ in the details but expected rain chances to persist
from Monday through the middle of the week as the upper level
trough shears out over or near Southeast Texas.

MARINE...
Again there is not much change in the forecast for the Upper Texas
Coast. Southerly winds should continue into the weekend. Winds have
increased to SCEC levels overnight and should continue this morning.
Winds should be decreasing Friday and into the weekend to closer to
10 knots. Seas currently running 4 to 5 feet and look for those seas
to slowly subside to around 2 to 4 feet for the weekend. Light winds
and low seas are expected for the start of next week.

Tide levels look to be near normal or a half foot above.

Overpeck

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      99  76  99  76 100 /  20  10  10  10  10
Houston (IAH)              96  78  97  78  97 /  20  10  20  10  20
Galveston (GLS)            92  83  92  82  91 /  20  10  20  10  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 7 PM CDT this evening for the following
     zones: Austin...Brazoria...Brazos...Burleson...Chambers...
     Colorado...Fort Bend...Galveston...Grimes...Harris...
     Houston...Jackson...Liberty...Madison...Matagorda...
     Montgomery...Polk...San Jacinto...Trinity...Walker...
     Waller...Washington...Wharton.

     High Rip Current Risk until midnight CDT tonight for the
     following zones: Brazoria...Chambers...Galveston...
     Matagorda.

GM...NONE.
&&

$$

Discussion...11
Aviation/Marine...42



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