Area Forecast Discussion
Issued by NWS Brownsville, TX

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694
FXUS64 KBRO 290525 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1225 AM CDT FRI JUL 29 2016

.DISCUSSION...Updated for latest aviation discussion below.
&&

.AVIATION...VFR is in place right now at the aerodromes and
should prevail through the remainder of the overnight hours.
However, a TEMPO for MVFR cloud decks has been added for a few
hours prior to sunrise. Tomorrow, VFR will continue as surface
winds become moderate and scattered cloudiness prevails at
higher levels. VFR is anticipated near sunset and for a few
hours afterwards Friday evening.
&&

.PREV DISCUSSION... /issued 259 PM CDT THU JUL 28 2016/

..Top Five Hottest July In Range as Month Closes As It Began...

SHORT TERM (Tonight through Friday Night):Main Concern might just be
for the remainder of the afternoon, as decent coverage of convection
has developed in good low level convergent zone across the King
Ranch with 40 to 50 percent coverage at 230 PM today. Other quick up
and down (pulse) cells scooting from southeast to northwest across
the Mid and Upper RGV into the Rio Grande Plains, and expect this
trend to continue with perhaps some brief clustering out in Jim
Hogg/Zapata by 4 PM or so, and may need to consider a brief increase
in chances for the 4 pm to 7 pm window.

Otherwise, convection has cleared the coastal counties of the Valley
and not much along the Rio Grande into Hidalgo, with mixed clouds
and sunshine and July heat pushing highs into the triple digits once
again along and west of US 281/IH 69C with near 100 all the way to
Harlingen.  This is a trend that will continue into Friday and well
beyond.

For tonight, things quiet down quickly after sunset.  GFS pretty
insistent on some cirrus spreading across the region after midnight,
even though a dry pocket on water vapor is approaching from the
east.  If the clouds to arrive, low temperatures may be similar to
this morning, a degree or two above an already warm forecast near 80
for the Valley and mid to upper 70s elsewhere, with just enough late
night southeast wind, 4 to 7 mph, to keep them from dipping too much.

For Friday, a tricky call whether to retain rain chances.  Moisture
thins into layers with fairly high RH to begin the day above 500 mb
but an increasing dry layer in the 850 to 550 mb layer which remains
steady state through the afternoon. Model guidance struggling to
generate 6 hour rain chances anywhere, so elected to roll a silent
10 percent for the daytime hour on land and at sea.  That said, 10
percent may well mean "stray showers" inland as surface winds will
be just light enough to allow a sea breeze.

Temperatures should be similar to today, so raised a degree or two
in all areas to match.

Friday night, the dry air thickens as has been the trend in recent
days with both GFS and ECMWF, so cleared skies a bit more and have
no mentionable rain anywhere. Still, with just enough southeast wind
and persistence kept low temperatures nearly identical to recent
days, near or just above 80 for the bulk of the population.

LONG TERM (Saturday through Thursday):The 500mb weakness will
continue to weaken as it drifts westward Saturday with 500mb
ridging building over Texas and the Western Gulf Sunday and next
week. As this ridging pattern takes hold it will offer no
significant rain chances. Deep layer dry settles over much of
South Texas with 850- 300 mean RH between 30-40% Mon- Thu coupled
this with subsidence provided by the ridge and rain chances will
be depleted significantly. As it is early August and we will be
heading into our wet season soon, one can not rule out the rouge
shower/tstm to form along the sea breeze.

The 12Z GFS and ECMWF 500 mb fields remain in good agreement showing
the mean ridge axis strengthening over the State and extending
across much of the Southern and Central Plains. Both models are also
trending drier for pops through day 7. Temperatures guidance
continues to nudge higher which is right on schedule for the average
hottest time of the year, first week of August. Inherited highs and
lows are already near to above seasonal averages so no need to
adjust at this time.

Also like clock work the tropics are waking up.  Two weak but
tractable tropical waves are located over the far Eastern
Atlantic...1700+ miles east of the Lesser Antilles. Both systems
have low probabilities of developing into tropical cyclones as they
move westward. These system pose no threat to the Gulf of Mexico at
this time.

MARINE:Now through Friday night...Light to moderate southeast flow
and a slight to moderate sea to persist through the period. Broad
and weak high pressure to combine with lower pressure in the Bay
of Campeche providing the modest onshore flow. Seas sitting on 3+
feet at buoy20 but down to 2.6 feet at buoy 02 (250 miles east of
South Padre). With slight decrease in surface gradient expect even
Laguna Madre to be generally 15 knots or less Friday afternoon.

(Saturday Tuesday): Broad surface high pressure to dominate
much of the Gulf of Mexico this weekend and next week.  This will
maintain a light to moderate S-SE wind and a slight sea. High
pressure in the upper as well as the lower atmosphere will keep
streamer shower activity to a minimum with only a few showers are
possible overnight and during the early morning hours.
&&

.BRO Watches/Warnings/Advisories...None.
&&

$$

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