Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 212008

Area Forecast Discussion
National Weather Service BROWNSVILLE TX
308 PM CDT Fri Oct 21 2016

.SHORT TERM (Tonight through Saturday Night): 500mb ridge across
the southwest United States and northern Mexico this afternoon
will move eastward across the state of Texas Saturday. Subsidence
will continue to increase across northeast Mexico and southwest TX
tonight into Saturday. Drier air continues to filter into the CWA
this afternoon in the wake of the cold front that moved through
the area overnight. This will provide a relatively cool night
across the Rio Grande valley and northern ranchlands tonight as
clear skies and light winds provide radiational cooling.
Temperatures will be slightly below normal tonight but near normal
Saturday and Sat night as the slightly cooler airmass quickly
modifies with diurnal heating Saturday and an onshore flow returns
Sat night.

For the coastal sections of the CWA...minor tidal washup is expected
this evening into early Saturday morning as the combination of wind
waves...swells and the astronomical high tide near 11 pm
tonight...will allow the surf to approach portions of the dunes
along the lower Texas coast after sunset tonight. A coastal flood
statement has been issued to address impacts along South Padre
Island and other beach areas along the coast tonight.

.LONG TERM (Sunday through Friday): The period begins with a
gradual transition back to somewhat "soupy" air but certainly
nothing like the record heat and fairly sweltering humidity we had
for the first 20 days of October. Overall, the area remains
underneath the persistent 500 mb ridge which slides back and forth
to provide subtle weather changes. On the whole, that ridge
ensures another above average week of temperatures with nothing
more than spotty precipitation, especially early in the period.

For Sunday, GFS remains bullish on a quick return of multi-layer
moisture with the ECMWF a bit slower to recover the column. But
each have a weak short wave denting the west side of the Gulf
ridge Sunday into Monday, which should be enough to eventually
bring isolated to scattered showers and perhaps a thunderstorm or
two back to the RGV/Deep South Texas beginning late Sunday night
and peaking Monday afternoon. GFS remains more bullish on
moisture and forcing Monday and even though the ECMWF shows a
similar 500 mb weakness the model is more disorganized with deep
layer moisture. Given that situation has hints of warm
frontogenesis (mainly via dewpoint recovery) have decided to lean
toward the wetter GFS which is also in line with most recent WPC
QPF trends on Monday.

Tuesday is a bit tricky. As Gulf ridge flattens the northern
Mexico ridge begins to rebuild. In between, enough 500 mb weakness
holds some moisture favoring the eastern third of the area
(Cameron to Kenedy) as well as the Gulf...and with northerly flow
tending to keep the energy in place expect some rain chances to
persist into Wednesday morning before turning into a sea breeze
type afternoon as deeper moisture begins to retreat/weaken over
the Gulf. For Wednesday night through Friday, the northern Mexico
ridge builds east to include all of the western half of Texas
including the Valley, and drier air follows. Increasing sunshine
and lower humidity kills off rain chances but also allows morning
lows to dip by the end of the period.

As for temperatures? Certainly no return to the century mark which
ended at an even 90 days for McAllen this year as of Thursday and
blew away the prior record by 12 days, but an initial steady state
of upper 80s to near 90 Sunday through Tuesday with enough cloud
cover to keep recovery "honest" but also insulate at night to
hold Valley lows close to or just above 70 for Monday through
Wednesday. Thereafter, with more sunshine despite slightly lower
1000-850 thickness values, expect a generally 88 to 92 by
afternoon and 63 to 68 by morning for Thursday and Friday. The
daytime temperatures will once again be well above average which
is low to mid 80s for late October.

One final thing to keep an eye on (see Marine discussion below) is
potential for a return to long period swells over the Gulf
beginning Tuesday and peaking Wednesday as strong high pressure
slides slowly off the U.S. east coast. A 8 to 9 second period
along with above predicted tides could bring more run-up onto
South Padre Tuesday and perhaps Wednesday before the predicted
tides fade back late next week.


.MARINE: Seas were near 8 feet with north to northeast winds near
18 knots with gusts to near 21 knots at buoy020 this afternoon.
The pressure gradient will begin to weaken across the coastal
waters tonight as surface high pressure settles across the Texas
coast. Strong northeast winds this afternoon will diminish tonight
as a result but seas will remain elevated across the offshore
waters. Will extend the small craft advisory for the Laguna Madre
through 6 pm as winds remain high across the lower TX coast. Will
also extend the SCA for the offshore waters through midnight
tonight...mainly for seas. Light to moderate northeast winds will
prevail across the coastal watesr late tonight and begin to veer
to the east Saturday as the surface ridge across east TX and the
western Gulf of Mexico moves eastward. Winds will eventually veer
to the southeast tomorrow night and continue to remain light
across the lower TX coast.

Sunday through Wednesday: For winds, period is quiet overall with
mainly southeast to east flow at 5 to 15 knots depending on time
of day and location. About the only concern will be how high the
combined seas may build as we move into early to mid next week as
1028+ high eases into the east coast with excellent fetch of
easterlies across the Gulf Monday through Wednesday. The swell
direction appears to be more east northeast to west southwest from
florida on out which could keep the highest push to the south of
our coastline but October is a favored time of year for buildup
around these types of eastern U.S. systems. Would not surprise to
see 5 foot seas with 9 second period at some point into the Lower
Texas Gulf waters but for now capped seas at 4 feet beginning
late Monday.


BAYVIEW/PORT ISABEL  64  83  68  88 /   0   0   0  10
BROWNSVILLE          63  85  71  89 /   0   0  10  10
HARLINGEN            62  87  66  90 /   0   0   0  10
MCALLEN              61  88  69  91 /   0   0   0  10
RIO GRANDE CITY      58  86  66  90 /   0   0   0  10
SOUTH PADRE ISLAND   75  83  78  85 /   0   0   0  10


GM...Small Craft Advisory for winds until 6 PM CDT this evening for

     Small Craft Advisory until midnight CDT tonight for GMZ150-155-



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