Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 181718 AAC
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1218 PM CDT Sun Jun 18 2017

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

&&

.AVIATION...VFR conditions today with breezy and gusty south
southeast winds under mostly sunny skies. Winds will die down
over night as gradient killing high pressure behind a front pushes
into North Texas. Southeast winds will be a skosh less on Monday,
in the light to moderate categories. The GFS MOS again wants to
bring in a few hours of MVFR ceilings Monday morning, whereas the
NAM MOS does not. The forecast sounding reveals a modest inversion
over BRO tonight, which will lower with a narrowing dew point
depression. The time height chart shows ample low level moisture.
Lower overnight ceilings have been fleeting the last couple of
nights, but believe stronger winds today will bring more moisture
inland, and the potential for low clouds may be better once winds
decrease and the boundary layer stabilizes overnight. Went ahead
with MVFR ceilings from roughly midnight to mid Monday morning,
though periods of thinner clouds and thus VFR breakouts will
likely be in the mix.

&&

.PREV DISCUSSION... /issued 748 AM CDT Sun Jun 18 2017/

DISCUSSION...Updated for latest marine discussion below.

MARINE...Hoisted a small craft advisory for all marine waters
for today. Looking for another day of fresh southeast to south
winds due to strong high pressure over the Gulf, including some
gradient tightening interaction with inland lower pressure. Wave
heights at buoy 42020 has been hovering around 7 feet.

PREV DISCUSSION... /issued 635 AM CDT Sun Jun 18 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Some passing high level clouds and moderate southeast
winds prevail across Deep South Texas this morning. VFR
conditions expected to continue for the next 24 hours as high
pressure remains in place. Breezy conditions will develop later
this morning, sustained winds around 20 knots with gusts
approaching 30 knots. Southeast winds will gradually decrease to
around 15 knots by late this evening. Light southeast winds
expected overnight with some low cloud decks returning.

PREV DISCUSSION... /issued 355 AM CDT Sun Jun 18 2017/

SHORT TERM (Today through Monday): A strong 500 mb ridge anchored
over the southwest United States and northern Mexico will provide
subsidence across Deep South Texas through the period. Above normal
to near record high temperatures expected across the area today and
Monday. High temperatures will range from the low to mid 90s near
the coast to triple digits across the western areas, mainly along
and west of US 281/I-69C corridor. Heat index values this afternoon
will be in the 105 to 110 degree range for a few hours over most
inland areas. A few places such as McAllen, Rio Grande City, and
portions of Kenedy county may even briefly reach into heat advisory
territory. However, will hold off on issuing a heat advisory and
will lean towards an Special Weather Statement for now.

Surface low pressure across West Texas interacting with high
pressure across the Gulf of Mexico will support moderate to breezy
southeast winds today. Overnight low temperatures will range from 75
to 80 under partly cloudy skies. Relative humidity values across the
Upper Valley will range from 25 to 35 percent this afternoon with 20
ft winds of 10 to 15 mph and with drying fuels. Thus, monitoring of
fire weather parameters should be sufficient for now, with no
supplemental fire weather products needed.

LONG TERM (Monday Night through Saturday): Confidence in the
extended forecast is not high as the medium-range global models
are varying widely in their solutions. For this portion of the
forecast, have leaned toward the ECMWF/Canadian solutions and away
from the GFS. Upshot of this is a tropical low that is to slowly
migrate northward over the west central Gulf early in the period,
which then moves onshore along the mid/upper Texas coast in the
Wednesday night/Thursday timeframe. Bulk of dynamics associated
with this low to remain offshore of the forecast area with only
slight chances of showers/thunderstorms for the land areas
Wednesday through Saturday. Trimmed chances of precipitation down
slightly each day during these five days due to the overall
confidence in the forecast. Otherwise, will see little change in
temps day-to-day as they are dominated by ample subsidence
associated with strong upper high pressure centered over the
southwest U.S./northwest Mexico. High temperatures to generally
remain above normal area-wide and will range from the lower 90s at
the coast, mid 90s over the lower/mid valley, and the upper
90s to around 103 out west.

MARINE (Today through Monday): Buoy 42020 reported
south-southeast winds around 21 knots with gusts near 25 knots
and seas of 5.6 feet with a period of 6 seconds at 03 CDT/08 UTC.
A small craft advisory remains in effect for all of the lower
Texas Gulf waters until 8 am. Otherwise, moderate to occasionally
strong southeast winds and moderate seas will continue through
today. Low pressure across west Texas interacting with high
pressure across the Gulf will support SCEC to marginal SCA
conditions on the Laguna Madre today and SCEC conditions the Gulf
waters today into early tonight. Marine conditions quickly improve
for Monday as light east to southeast winds prevail across the
coastal waters as the pressure gradient weakens.

Monday Night through Thursday: Seas over the northwest Gulf to
build Monday night through Tuesday night before leveling off in
response to a tropical low moving north over the western Gulf.
Seas to begin to subside Wednesday night/Thursday as the tropical
low moves onshore over the mid/upper Texas coast. Small Craft
Advisory conditions are likely Tuesday night through Wednesday
night as larger swells from the tropical low move toward and
affect the lower Texas coast waters.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory for winds until 6 PM CDT this evening for
     GMZ130-132-135.

     Small Craft Advisory until 6 PM CDT this evening for GMZ150-155-
     170-175.

&&

$$

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