Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 222338 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
638 PM CDT Sat Jul 22 2017

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


.AVIATION...VFR conditions to prevail across the RGV and all of
Deep South Texas. Surface high pressure over the Gulf of Mexico
will continue to interact with lower pressure over West Texas
maintain and strong pressure gradient this evening into Sunday.
Gusty conditions persist through the evening then become less
frequent overnight before redeveloping Sunday afternoon. Gusts
between 20-30 knots are expected.


.PREV DISCUSSION... /issued 310 PM CDT Sat Jul 22 2017/

SHORT TERM (Now through Sunday Night): Mid summer heat combined
with the Valley Wind Machine will be the dominant story again
Sunday afternoon, with enough overnight winds tonight especially
to keep minimum temperature up a hair...similar to this
morning...on Sunday with perhaps a very slight decrease by Monday

The features remain the same as previously discussed; weak upper low
centered near southern Louisiana (but underneath the sprawling 500
mb ridge across the entire southern third of the US) will
continue to fill while nudging into southeast Texas Sunday and
Sunday night. Deepest precipitation-producing moisture will remain
well north of the Valley, mainly from southeast Texas through
Louisiana/Mississippi/Alabama, but similar to today some re-firing
convection may allow some cirrus to spill southwest in 200-400 mb
northerly flow to reach the Valley.

If some of the cirrus can, it could knock a smidge off the afternoon
temperatures on Sunday.  GFS shows some thickness of the cirrus
overnight and Sunday, so owing to perhaps a period or two of dimmed
sunshine, lowered max temperatures a degree from this afternoon -
but nothing that will really be notable. The overall sense of the
sky will be mostly sunny with a few cumulus and the scattered cirrus
above, and mainly clear at night.  As for the nighttime sky, may see
some more patches of fragmented cumulus on the stronger low level
jet which is typical in such a pattern...but other than a few areas
that could go broken across the ranchlands not expecting any impact.

Otherwise, expect gusty winds to crank a little quicker Sunday
morning, with frequent gusts to or over 30 mph from noon through 6
PM (later farther west) but falling shy of wind advisory levels.
Winds on Sunday night, just like this evening, will still be fresh
through midnight but could dip a bit lower by Monday morning.

LONG TERM (Monday through Saturday): The weekend weather will
continue into the new work week as hot temperatures, dry weather,
and breezy conditions lingering on. The cause of this is the
persistent ridging across the Desert Southwest with continued
subsidence suppressing any rainfall chances. Temperatures Monday
will once again top out from the lower to 90s to around 100F for
the coastal counties, with reading from 101 to 106 for other
locations in the RGV and Ranchlands. Heat index values will still
be in the 105 to 110F range.

Models continue to hint at a brief mid level pattern change
Tuesday through Thursday as a weak H5 low/open wave meanders
along the Texas Gulf coast early in the period before it moves
west over the region around the periphery of the high pressure
ridge. This subtle push back against the ridge should allow a
small surge of tropical moisture to drift into the Deep South
Texas and the RGV. However, the best moisture levels look to
remain across Northern Mexico, staying south of us. Furthermore,
long term models have flipped on POPs with the GFS trending drier
compared to the now wetter ECMWF. With this continued uncertainty,
have generally kept the on-going 20 to 30 POPs. Meanwhile, the
small uptick in moisture should help drop temps a couple of
degrees, however, readings will still be mostly in the 90s to
around 103. Heat index values will have to be monitored closely as
the hot temps, combined with more moist air, could allow for
indices near or over 111 degrees, which would put us near heat
advisory levels.

By the end of the period, the aforementioned ridge will shift
south and east in response to the tropical system in the Eastern
Pacific. This will allow the ridge in amplify over Texas and
effectively shut out any tropical moisture. Temperatures will
also quickly become hot once again, with readings possibly even a
degree or two higher than what is occurring currently.


Now through Sunday Night: Caution conditions near 20 knots with a
few gusts solid on Laguna Madre and are close to advisory but
just shy in the bay with a tad higher at the Land Cut (King Ranch)
area which is pretty common in this pattern. Despite warm Gulf
waters (mid 80s) marine layer is holding enough to keep winds
fresh but not too high, near 15 knots. Gulf seas have held at 3
feet today, nearly all due to wind waves, some "very steep" which
is a bear for offshore fishers.

The news remains bleak for fishers in the Gulf for the next 48 hours
with wind and seas continuing to be a nuisance.  Persistence of
south/southeast flow and the low level jet tonight will bring Gulf
winds solidly into caution (15 to 20 knots and gusty) range and
perhaps close to advisory levels, with seas building to 4 feet.
Laguna winds will stay up this evening before settling back, then
the higher winds will flip to the Laguna Sunday afternoon with
caution level for sure and advisory (wind) a pretty good bet for
afternoon. A similar setup Sunday night, with seas possibly reaching
5 feet - but much of the seas due to wind waves (at least 4 feet)
with steep to very steep values in the open waters.

Best fishing will be on Laguna Madre during the wee hours (pre-dawn)
both Sunday and Monday.

Monday through Wednesday: High pressure over the northeastern
Gulf will continue to interact with a surface low pressure system
over the Plains through early Tuesday. As such the surface
pressure gradient will remain tight. Southerly winds will
continue to range near 15 to 20 kts with seas from 4 to 6 feet.
with Small Craft Exercise Caution conditions continuing. The
surface high will become more centered over the Gulf by mid week,
decreasing the pressure gradient and allowing seas and winds to


BAYVIEW/PORT ISABEL  80  96  80  96 /  10  10   0  10
BROWNSVILLE          79  94  79  94 /  10  10   0  10
HARLINGEN            78 101  78 100 /  10  10   0  10
MCALLEN              80 103  80 103 /  10  10   0  10
RIO GRANDE CITY      79 103  79 104 /  10   0   0  10
SOUTH PADRE ISLAND   82  91  82  90 /  10  10   0  10




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