Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 152345 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
645 PM CDT Tue Aug 15 2017

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


.AVIATION...Strong southerly winds to slowly diminish this evening
and overnight with gust becoming less frequent a few hours after
sunset or by midnight in the vicinity of KMFE. Added gulf moisture
with the southerly flow and a developing low level inversion will
allow for lower MVFR clouds to develop and stream northwards. Hi-
resolution and global models suggest low probabilities of brief
MVFR cigs at times overnight. This will be mentioned in TEMPO
groups after midnight and before sunrise. Cumulus field Wednesday
may be more extensive with a BKN VFR deck in the morning becoming
SCT in the afternoon as stronger winds mix through the boundary
layer moisture. Expect wind gusts in the 25-30knot range again


.PREV DISCUSSION... /issued 242 PM CDT Tue Aug 15 2017/

SHORT TERM (Now through Wednesday Night): No significant changes to
the short term forecast as a strong H5 ridge remains perched over
much of the Southeastern U.S. and Eastern Gulf of Mexico. This will
allow for mainly hot, rain-free weather to continue through
Wednesday night as subsidence and dry air remain in the mid levels.
However, this mornings 12Z sounding did indicate a slight increase
in precipitable water with a report of 1.75".  Meanwhile, this
afternoon, the experimental and non-operational GOES-16 derived
Total Precipitable Water satellite imagery continues to show a small
surge of moisture increasing over the offshore Gulf Waters with even
a few isolated showers noted on radar. Current thinking is that this
moisture is getting wrapped around the periphery of the surface high
over the eastern Gulf.

Model guidance continues to indicate that additional, albeit small,
fluxes of moisture will move northward through the region tonight
and on Wednesday. Forecast soundings show an uptick in PWATs with
values increasing to 1.80" to around 2.00" by Wednesday afternoon.
While it is doubtful that any precip will form due to the
exceedingly dry air aloft and lack of forcing, the moisture could
raise dewpoints enough at the surface on Wednesday to be concerned
about warmer heat index values. Indeed, heat indices will likely
reach upwards of 111F or higher over a small portion of the Middle
RGV in Hidalgo and Starr Counties. Later shifts will need to monitor
for increasing trends to see if heat advisories are needed.

LONG TERM (Thursday through Tuesday): A 500mb ridge will build over
Texas on Thursday into Friday. The pressure gradient begins to relax
Thursday as surface high pressure moves across the central Gulf of
Mexico. Some convection is expected to develop around the periphery
of the mid-level ridge Friday into Saturday. The latest GFS/ECMWF
are in agreement with an inverted 500mb trough moving westward
over the central and western Gulf of Mexico Sunday into early
next week. This mid-level feature combined with daytime heating
and increasing moisture will support some isolated seabreeze
convection Sunday through Tuesday. Above normal temperatures
expected to prevail across the area through the period.

MARINE (Now through Wednesday Night): Buoy 42020 was reporting
moderate south winds around 15 knots with gusts to near 20 knots and
3 to 4 ft seas at 1 PM CDT. Meanwhile, gusty S to SSE winds of near
20 to 25 knots continue across the Laguna Madre this afternoon with
a Small Craft Advisory still in effect until 9 PM tonight. Small
craft should exercise caution over the offshore waters east of Padre
Island through the remainder of the afternoon. The surface pressure
gradient will remain tight through at least Wednesday night due to
the interaction between high pressure over the Eastern Gulf and low
pressure over West Texas and the Southern Plains. Additional small
craft advisories may be need for the bay waters tomorrow and
possibly overnight for the Gulf waters.

Thursday through Sunday...The pressure gradient begins to weaken
across the western Gulf of Mexico on Thursday. Moderate southeast
winds should prevail across the lower Texas coast on Thursday.
Surface high pressure across the central Gulf of Mexico Friday
into the weekend will provide light to moderate southeast winds
and low seas across the western Gulf of Mexico.


BAYVIEW/PORT ISABEL  81  93  81  95 /  10  10  10  10
BROWNSVILLE          80  95  79  97 /   0  10   0  10
HARLINGEN            79  99  79 100 /   0  10   0  10
MCALLEN              81 102  81 102 /   0  10   0  10
RIO GRANDE CITY      78 103  79 104 /   0  10   0  10
SOUTH PADRE ISLAND   82  89  82  91 /  10  10  10  10


GM...Small Craft Advisory for winds until 9 PM CDT this evening for



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