Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 240603 AAC

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
103 AM CDT Mon Jul 24 2017

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


.AVIATION...Skies shoudl remain mostly clear overnight, except for
some cloud thickening noted currently right around KHRL. Any
thickening beyond SCT will remain temporary throug sunrise. Dry
air sloft will keep CU development to a minimum through the
afternoon. Gusty south winds forecast again through the day
Monday, with winds from 140 to 160 degrees at 20kts sustained with
gusts nearing 30 during the afternoon.


.PREV DISCUSSION... /issued 847 PM CDT Sun Jul 23 2017/

DISCUSSION...Updated for latest marine discussion below.

MARINE...Latest buoys and TCOON sites indicate that winds remain
near or exceeding small craft advisory levels thus will extend the
SCA for the Laguna Madre and near shore coastal waters until
midnight when models suggest the winds decoupling sufficiently
allowing winds to drop below criteria.

PREV DISCUSSION... /issued 643 PM CDT Sun Jul 23 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR conditions continue through the night and again
Monday. Low level moisture and a steady southerly winds to allow
for a few lower clouds overnight with a patch or two of brief MVFR
cigs in the vicinity of KMFE around sunrise. Stronger low level
winds to gradually diminish after sunset with stronger gusts
persisting between 04-05Z at KMFE. Pressure gradient weakens
slightly for Monday with gusts of 20-25 knots.

PREV DISCUSSION... /issued 337 PM CDT Sun Jul 23 2017/

SHORT TERM (Tonight through Monday Night): The seemingly ever persistent
H5 high pressure ridge across the Four Corners region will continue
to dominate the weather across the CWA through the short-term
forecast. Meanwhile, a weak mid level low pressure wave continues to
continues to meander over the Northern Gulf coast near Louisiana.
Although models previously showed the low generally filling in as it
meandered west across the Texas coastline, current solutions
indicate that while it will weaken, it will now well remain north of
the RGV. The H5 ridge then appears to dig further south tonight and
Monday the main trough over the Eastern CONUS deepens. The trough
will generally absorb the weak low pressure wave, with the ridge
keeping it to the east of the Deep South Texas.

As such, this will limit the amount of return moisture on Monday
with models only indicating some slight increase in the mid levels
as weak troughing moves westward across the Bay of Campeche. Given
this, the forecast will continue to remain hot and dry. Overnight
lows will continue to run in the mid 70s to lower 80s, with steamy
highs on Monday still ranging from the 90s near the coast to near
106F across the Upper Valley and Western Ranchlands. Heat index
values will continue to be a concern with 105F to 110F or a smidge
higher possible. Winds will continue to be breezy on Monday, but
should not be as gusty as the last couple of days.

LONG TERM (Tuesday through Sunday): "La Canicula"...the Dog Days
of Summer...continue right in the heart of its season (coinciding
with Sirius, the dog star, rising with the sun) which extends
through August 11th astronomically. The Canicular pattern features
a dominant southwest U.S. ridge that often extends into south
Texas and northern Mexico, and that`s exactly what the mean
pattern does through the end of July.

The only fly in the ointment comes early...Tuesday and
Wednesday...when mixed layer moisture continues to show up on
global models. In the big picture, however, the moisture is
associated with little more than a tail of weak vorticity
leftover from the late weekend/early weekend upper level trough
that lurked along the northwest Gulf coast near southern
Louisiana. Both GFS and now the ECMWF show the "best" moisture at
the mixing level with more dry air than moisture above and little
to no vertical motion. That said, with southeast flow gradually
receding, though still in place a bit, cannot rule out isolated
showers/thunderstorms mainly from after midnight in the Gulf and
sliding onshore in Tamaulipas then streaming/developing northward
into the Lower Valley around or after sunrise before tending to
dissipate to 10 percent or less coverage farther west by afternoon
and end near the coast by early afternoon in the usual diurnal
pattern (while some coverage continues over the Gulf). Tuesday
seems to be the better day for rain chances...relatively
speaking...but still enough moisture in the 850 to 600 mb layer
mainly during the morning to keep a persistent forecast of slight
chance near the coast.

Thereafter, the Canicular ridge takes over and sprawls into
northern Mexico through Saturday which ends any threat of rain and
brings perhaps the hottest area-wide temperatures of this July to
the area. Atmospheric thermal parameters combined with climatology
and dry air through the column suggest 104 to 106 for the
mid/upper Valley through Zapata County, with 98 to 102 elsewhere
except along the coast. On Sunday, the GFS begins retrograding the
ridge from the four corners into the Great Basin while doing the
same with a meridional summertime east coast trough...which
strengthens northerly flow and actually brings the tail of frontal
moisture to the Valley. ECMWF has a somewhat weaker tail and holds
off until Sunday night, so for now elected to hold the status quo
of the forecast which is light east to southeast winds and still
plenty hot with no mentionable rain.

The drier atmospheric air will be enough to bring dewpoints down
and keep heat index just under advisory levels (111) which has
been the story for much of this month; 105 to 110 in general
(highest near the river from McAllen east) is the story...though
without the breeze wicking away the moisture it may actually feel
worse. For the beaches...the moderate longshore current will
continue through Tuesday or Wednesday before fading as waves/seas

MARINE: Now through Monday Night: At 2pm, Buoy 42020 was
reporting south winds of 15 to 20 knots with seas holding near 5
feet. The surface pressure gradient remains tight this afternoon
as broad high pressure over the Eastern Gulf continues to interact
with low pressure across the Plains. As such, moderate to strong
south winds will continue through the remainder of the afternoon
into the early evening with a SCA for winds across the Laguna
Madre and the nearshore waters in place. Conditions will improve
tonight and on Monday as the high pressure moves west into the
central Gulf with more SCEC conditions likely.

Tuesday through Thursday Night: Winds and seas will be on the
decline as central and eastern Gulf ridge spreads west toward the
Texas coast, and surface trough across west Texas weakens as well
(1006-1010 mb) so potential caution conditions (15 to 20 knots)
Tuesday afternoon and perhaps over the Gulf Tuesday night will
fade to 15 knots or less Wednesday, and 10 knots or so by
Thursday. Seas will drop equivalently to 2 to 3 feet by the end of
the period...making Thursday and perhaps into the weekend much
better fishing/boating conditions than was seen this weekend.




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