Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 200445
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1145 PM CDT Mon Jun 19 2017

.AVIATION...
Cirrus remains over the area and a few weak showers continue to
develop. Moisture levels slowly drop overnight but PW values look
high enough through 09z to generate some pesky showers over mainly
the eastern TAF sites. Winds are expected to become north later
tonight and gradually increase toward sunrise. Moisture levels
look sufficient for a few showers again on Tuesday afternoon. Weak
capping is noted at 700 mb so will forego mentioning in the TAFS.
Fcst soundings shows the moisture profile drying toward evening
with more cirrus possible. Winds will remain moderate to strong
toward the coast late Tuesday aftn into Tuesday night as the
disturbed weather over the Gulf shifts west. 43

&&

.PREV DISCUSSION... /ISSUED 950 PM CDT Mon Jun 19 2017/

UPDATE...
Save for a lone thunderstorm rolling across Wharton and Jackson
Counties this evening, all earlier convection along the sea
breeze has dissipated. Lowered PoPs for the remainder of the
evening to reflect these trends, with minor updates made to
temperatures and dewpoints based on observational trends. Expect
overnight lows to fall into the mid 70s to low 80s under partly
cloudy skies.

Regarding Potential Tropical Cyclone Three, satellite presentation
for this disturbance remains largely unorganized with most of the
convection associated with this disturbance located well east of
the center. The center of the disturbance itself is still very
difficult to ascertain with several vorticity lobes (or areas of
spin) over the central Gulf offering misleading representations of
where this center may be. As a result, the forecast for Potential
Tropical Cyclone Three will see continued refinements over the
next few advisories and Southeast Texans (especially those with
marine interests) are asked to keep up with the forecast over the
next few days.

With 18Z and preliminary 00Z guidance showing a rather broad
windfield in association with this system as it moves towards the
west-northwest over the next few days (and consistent with the
National Hurricane Center), have updated the wind grids Tuesday
through Thursday morning to reflect at least some influence from
this system over the offshore (20-60 nautical mile) waters.
However, even with these adjustments, no Tropical Storm Watches or
Warnings are currently in effect for any of the coastal waters
between the Matagorda Ship Channel to High Island.

Huffman/43

PREV DISCUSSION... /ISSUED 349 PM CDT Mon Jun 19 2017/

DISCUSSION...
Major question of the forecast is obviously Potential Tropical
Cyclone 3, located north of the Yucatan Peninsula, currently given
an 80 percent chance of development in the next couple of days by
NHC. At this time, think any developing storm will be heavily
sheared with most impacts to our east. However, any western
deviation in track would begin to slide impacts into our area - it`s
a close call, so continue to monitor the forecast.

SHORT TERM [Through Tonight]...

Through tomorrow, the typical summertime pattern should reign for
most of the area, though by Tuesday afternoon falling heights aloft
should help allow for increased convection over the Gulf waters and
potentially the immediate coast. In the meantime, very isolated
activity along the seabreeze is possible into the evening hours
before the loss of sun wanes activity.

MEDIUM TERM [Tuesday Through Wednesday Night]...

The most impactful portion of the forecast is also the most
uncertain. Fortunately, the guidance envelope has shrunk today.
Still, the west outliers come ashore around Galveston Bay, so we are
not totally out of the woods yet. If we were to assume a west
outlier landfall, the storm should still be heavily sheared to the
east, keeping much of the impacts east of the Houston metro.

The forecast is based off of a very reasonable track presented
through collaboration with NHC and WPC, which occurs even more to
the east of our area. Some borderline likely PoPs crop up late
Wednesday along our eastern border, but the vast majority of the
area will see a chance of rain or drier. Similarly, it may be a bit
breezy our of the northeast on the west side of the cyclone, but
nothing excessive - it may be not even be quite at a level that
would necessitate a wind advisory.

Now, with all that said, we still lack a true center, which makes
model guidance considerable more unreliable that usual, as specific
models may or may not accurately determine where the eventual center
will take hold. If you`ve been watching the satellite (especially G-
16) today, you`ve seen multiple little whorls near or ejected from
the convective mass over the Gulf. None so far have taken as a more
dominant center of circulation. Once a more dominant center emerges,
guidance should become more reliable. Until - and even after - then,
continue to monitor the forecasts, and still stand ready to take
necessary precautions in case of a move to the west, as rainfall of
6 to 8 inches or more will be possible in such an instance.

LONG TERM [Thursday Through Monday]...

Now, regardless of guidance, this potential TC looks to accelerate
northeast of the area Friday, leaving us with a return to a more
typical June atmosphere. The big change from the past several days,
however, is that the southwestern US ridge will be weaker, and
though the Atlantic subtropical ridge will be working to build
westward, it will largely set up deep onshore flow, which should
boost precipitation potential. So, rather than the very dry weather
we`ve seen lately, scattered showers and storms should again return
to be more the rule. The retreat of the southwestern US ridge should
also result in slightly cooler temperatures, with highs closer to 90
degrees than the middle 90s.

AVIATION [18Z TAF Issuance]...

Convection from the overnight MCS is still trying to move south into
the CWA early this afternoon, but not finding much success (given
the strong cap over the region). However will maintain a mention of
VCTS/VCSH for most sites through the late afternoon/ early evening
as outflow boundaries (moving south) and the sea-breeze (moving
north) possibly interact. Thereafter, much drier conditions will
prevail as NE winds develop overnight/early to-morrow morning and
persist. 41

MARINE...

Winds will continue to slowly shift to the E/NE tonight as the area
of disturbed weather approaches in from the southern/central Gulf.
Wind speeds should begin to increase over the coastal waters during
the afternoon tomorrow (with seas following suit). Caution/Advisory
flags are likely by this time but could be upgraded/tweaked depend-
ing on the track/evolution of the Gulf system through Thurs. Marine
interests and mariners should stay abreast with the latest updates.
Onshore winds are expected to return to the area by the latter part
of the week. 41

TROPICAL...

Implications of the potential tropical cyclone north of the Yucatan
are discussed in the middle week section above.

Potential Tropical Cyclone Two is now Tropical Storm Bret, located
in the Atlantic Ocean about 125 miles southeast of Trinidad.
Expectations continue for it to move to the WNW, along or just north
of the South American coast. It is also expected to struggle with
shear in the Caribbean Sea and travel at a very low latitude. It is
very unlikely to impact our area. But, until dissipated, a storm to
the south and east is one to be monitored.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      76  94  75  95  75 /  10  10   0  10  20
Houston (IAH)              77  95  78  94  76 /  20  10  10  30  40
Galveston (GLS)            82  90  82  89  81 /  10  30  30  40  50

&&

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

$$

Discussion...14
Aviation/Marine...43



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