Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 132336 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
636 PM CDT Sun Aug 13 2017

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

&&

.AVIATION...High confidence that VFR will prevail over the next 24
hours due to high pressure aloft and a relatively dry atmospheric
column. Some signal in the prog soundings that fleeting cloud
decks may develop around 2,000 ft. AGL overnight, near the base of
the nocturnal inversion. No prevailing CIG expected, however. SSE
winds remain elevated (for the season) due to an enhanced pressure
gradient between a surface high over the Gulf and thermal low-
pressure troughing inland over Mexico.

&&

.PREV DISCUSSION... /issued 256 PM CDT Sun Aug 13 2017/

SHORT TERM (Now through Monday night): Morning sounding showed all
moisture is trapped in the lowest 3000 feet, and this is
corroborated by all 12 or 13 clouds that have formed in the region
today. H5 ridge will vary little across the area during the next 36
hours, keeping cloud cover to a minimum and keeping temperatures
above normal. Conditions will remain breezy through the rest of
today and again tomorrow, as the Gulf surface ridge interacts with
the thermal low across northeast Mexico.

LONG TERM (Tuesday through Sunday): Have not made any significant
changes to the long term forecast as broad mid-level high
pressure continues to dominate the weather pattern through the
week. With this ridge in place, temperatures will continue to
range above normal with triple digit highs from near I-69E/HWY 77
and west into portions of the Upper RGV and Western Ranchlands
near Zapata. Only near the the coastal regions will temps be in
the mid to upper 90s. Meanwhile, humidity values will still be
high and heat index values ranging to near 115F cannot be ruled
out for portions of the RGV on Tuesday and Wednesday. Heat
advisories may be needed. However, much of this will depend on
dry air mixing down given the breezier conditions during this
time frame.

These stronger winds will develop due to a heat low over the the
higher terrain of northern Mexico interacting with high pressure
over the eastern Gulf to strengthen the pressure gradient.
Sustained winds over the land areas during the day Tuesday and
possible Wednesday will become moderately strong, but should
remain below advisories level. At night, after the land
stabilizes, a strong 30 to 40 knot 850mb jet will develop, off the
surface and winds will then pick up over the unstable offshore
waters.

Meanwhile, dry weather will continue through at least Thursday as
the pressure gradient lessens with surface high pressure becoming
more centered over the Gulf although it will still likely be
breezy through the end of the period. However, rain chances could
return by Friday and Saturday as a weak inverted trough moves
northwest-ward over the Bay of Campeche and brings a minor surge
of moisture. If wind weaken enough and there is enough tropical
moisture in place, then a few seabreeze induced showers could
form on Friday and Saturday. However, given the uncertainty and
overall lack of moisture and forcing, have opted to keep only a
slight chance for showers.

MARINE:

Now through Monday: Conditions remain stable across the Gulf
waters, with swells between 3 and 4 feet. Gradient between the
Gulf ridge and thermal low in mexico will keep winds elevated
through the short term. Breezy conditions will continue for the
Laguna through sunset, before shifting offshore overnight. Breezy
conditions will return tomorrow morning for the Laguna, with
latest forecast slightly increasing the peak winds to near 20
knots, which would require advisories for the afternoon.

Tuesday through Friday: A heat low over northern Mexico will be
interacting with high pressure over the eastern Gulf to start the
period. Winds will remain elevated over the Laguna Madre and the
nearshore Gulf waters Tuesday and Wednesday with possible small
craft advisories need for southerly winds around 20 to 22 kts with
higher gusts. At night, the winds will flip, with these higher
values over the far offshore waters. Seas will also come up as
well, with 4 to 6 ft winds waves expected, although they could be
slightly higher on Wednesday. By Thursday and Friday, the
gradient will weaken as high pressure become more established over
the Gulf with more moderate winds and seas returning.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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