Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 190938

Area Forecast Discussion
National Weather Service Brownsville TX
438 AM CDT Sat Aug 19 2017

.SHORT TERM (Today through Sunday): Looking for any window for
increasing moisture that might bring a chance of rain to the CWA but
the stubborn 500mb Ridge is holding tight.  Impressive looking 25H
low over the S Florida and SE Gulf will be very slow in moving west
against an equally strong ridge.  This will likely keep the forecast
status quo with persistence the best forecast for the weekend.  Any
showers will be limited to the outer coastal waters with very low
probabilities of any sea breeze activity as plenty of subsidence and
mid level dry air remain in tact and overhead. Otherwise...the heat
continues with moderate afternoon breezes to limit the oppressiveness.
Maximum temperatures yesterday were 2-3 degrees above guidance and
forecast so have bumped up highs the next few days. This will impact
the heat indices with Sunday`s heat index values approaching 109-112
for at least a few hours across most of the populated RGV. No change
in the overnight lows with the sultry August upper 70s to lower 80s

.LONG TERM (Sunday Night through Friday): The long term portion of
the forecast is becoming increasingly interesting. The dominant
meteorological player during this period will be an inverted 500
mb trough with nested closed 500 mb low pressure that will slowly
advance towards Deep South Texas and the Rio Grande Valley from
the east, move over this region, and then west into north-central
Mexico. Isolated to scattered showers and thunderstorms will be
generated by this trough/low complex as it moves over the BRO
CWFA. What is interesting is that this same complex, in addition
to producing beneficial rainfall, will maintain an absence of 500
mb high pressure over the western Gulf of Mexico to the extent
that Tropical Storm Harvey, now over the eastern Caribbean Sea,
may directly affect this region. Indeed, multiple runs of 06Z
model guidance suggest Harvey will move over the Yucatan Peninsula,
into the Bay of Campeche, and then somewhere over the western
Gulf of Mexico, especially the coastal waters of neighboring
Tamaulipas. The 00Z run of the GFS takes this even a step further,
showing an organized tropical system making landfall over the
northern half of Tamaulipas and then moving rapidly north-
northwest through the central portion of the BRO CWFA. As this
scenario is Friday night through Saturday and beyond the official
end of the long term forecast period, it is way too early to
assume this scenario is definitive. For now, will focus on the
potential for rainfall from the trough/low complex and continue to
watch the progress of Harvey and analysis from the National
Hurricane Center.

.MARINE (Today through Sunday): Fair marine weather to continue this
weekend with a light to occasional SE wind.  At 2 am, seas were
around 3 feet at Buoy020 with southeast winds around 12 knots
gusting at 15 knots. Little change in these tranquil conditions are
expected with broad surface high pressure extending across the gulf
and weak low pressure inland.  A very isolated shower well offshore
this morning...could see a few more in the outer waters Sunday
morning with a large upper level low pressure area moving into the
Eastern Gulf.

Sunday Night through Friday: Light to moderate winds and low to
moderate seas are expected due to the influence of surface high
pressure. Although no Small Craft Exercise Caution or Small Craft
Advisory is anticipated during the forecast period, Cautions or
Advisories (or worse) may be needed beyond the official end of the
forecast period due to Harvey, currently a tropical storm over
the eastern Caribbean Sea. Please refer to the long term forecast
discussion above for more details.

BAYVIEW/PORT ISABEL  97  80  97  80 /  10  10  10   0
BROWNSVILLE          97  79  97  79 /  10  10  10   0
HARLINGEN           100  78 100  78 /  10  10  10   0
MCALLEN             104  81 104  80 /   0   0   0   0
RIO GRANDE CITY     104  79 104  78 /   0   0   0   0
SOUTH PADRE ISLAND   89  82  89  81 /  10  10  10   0



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