Area Forecast Discussion
Issued by NWS Brownsville, TX

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805
FXUS64 KBRO 201117
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
617 AM CDT Tue Jun 20 2017

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

&&

.AVIATION...Aside from some patchy MVFR cigs early this morning,
VFR conditions to prevail through the TAF period. May see an
isolated shower or thunderstorm mainly east of Highway 69E early
this afternoon. East to southeast winds gusting to 18 knots at a
maximum this afternoon. Otherwise, light/variable winds early this
morning and again after 06Z tonight.

&&

.PREV DISCUSSION... /issued 433 AM CDT Tue Jun 20 2017/

SHORT TERM (Today through Wednesday): Forecast the next couple of
days to largely be driven by path/effects of Potential Tropical
Cyclone Three (TS Cindy...if/when named at some point). For today,
Deep South Texas to remain under northeast flow aloft in response to
strong high pressure centered over the southwest U.S. and PTC3 over
the northern Gulf of Mexico. The 00Z NAM and GFS continue to show a
band of moisture rotating around a trough of low pressure over the
northwest Gulf today. The latest run of the NAM is showing any
precipitation generated from this moisture to remain limited over
the coastal waters while the GFS generates precipitation area-wide.
Given apparent lack of dynamics, will scale back chances of
precipitation mainly over the western third of the forecast area. Am
not highly confident that precipitation will even develop over
lower/mid valley locations, so will leave just slight chances in
those locations for now. Otherwise, hot conditions will return again
this afternoon with highs ranging from the lower/mid 90s at the
coast with upper 90s to around 103 inland. Heat index values will
range from in the 101 to 106 degrees.

LONG TERM (Wednesday Night through Monday) Model guidance and
the latest NHC forecasts continue to move Potential Tropical
Cyclone Three towards the northwest Gulf Coast as it meanders
slightly through the Central Gulf. The low still remains
disorganized with the center generally removed from the area of
heaviest rainfall and strongest winds which are to the northeast.
This tropical low will continue to generally move towards the NW
Gulf coast, near the Texas and Louisiana state boarders and well
north of here, Wednesday night into Thursday morning. At this
point models indicate that the subtropical ridge of high pressure
over Texas and the Desert Southwest and the Bermuda High will
strengthen and push the low towards the ARKLATEX where in get
picked up by the next developing 500mb trough over the Northern
CONUS.

With the current track of PTC3 staying to the northwest, impacts
to the RGV will be generally limited to the immediate coastal
areas and Gulf waters. The main concern will be continued
increased swells generating dangerous rip currents along the
beaches at SPI. As such, do expect at least a moderate to high
risk of rip currents Wednesday night into Thursday before swells
drop off somewhat. With the higher swell, there could be some
beach erosion and run-up of water to the dunes which would lead to
minor coastal flooding. This will continue to be monitored
closely over the next day or so.

Rainfall chances continue to be minimal at best with this system.
Although, if enough moisture does wrap around the tropical low to
the west, the coastal counties and Gulf waters will have at least
a slight chances for some precip.

Heading into Friday and through the weekend, the weather pattern
shifts again as an inverted mid level trough moves across the Bay
of Campeche bring a surge of moisture with it. This feature will
bring Deep South Texas and the RGV its best chances for any kind
of widespread rainfall, with chances continuing possibly into next
Monday as well. As far as temperatures go, the above normal heat
will continue and highs Thursday and Friday will be near or above
recording breaking. Temperatures will drop off a few degrees for
the weekend with increased moisture and possible rain chances.

MARINE:

Today through Wednesday: At 2 am CDT, waves at buoy 42020 were
2.3 feet with modest east winds. Seas to build through the period
in response to westerly swells from Potential Tropical Cyclone 3
(Tropical Cyclone Cindy...if/when named). Small Craft Should
Exercise Caution conditions to develop over the lower Texas coast
Gulf waters this afternoon with Small Craft Advisory conditions
likely sometime tonight/Wednesday.

Wednesday Night through Saturday: Potential Tropical Cyclone 3
will be moving across the Northwest Gulf Waters Wednesday night
into Thursday. Increased swells will continue with Small craft
Advisories likely through early Thursday morning. After PTC3 moves
inland sometime Thursday, seas will begin to subside. However,
this will be short lived as the pressure gradient tightens and
winds and seas once again increase to small craft advisory
criteria Friday into Saturday. There are still some small chances
for rainfall Wednesday night into Thursday, however better chances
will return Friday into Saturday.

FIRE WEATHER...Dry conditions will continue on Wednesday and
Thursday as rainfall chances decrease due to the track of PTC3 now
moving more north and west towards the Texas/Louisiana state
border. Meanwhile, humidity values will drop into the upper teens
and lower 20 percent range for portions of the Upper RGV and NW
Ranchlands. RH values will be even be low, mid 20s to lower 40s,
towards the coast. The 20-foot wind are not expected to be strong
but gusty conditions in the afternoon may result in some elevated
fire threat. Additionally, high temperatures Wednesday and
Thursday approach or exceed 100 degrees across the Lower Valley
and range 104-109 in the Upper Valley and Western Ranchlands.
Friday could be another day of concern as temperatures could be
warmer, with 20-foot winds increasing to near critical thresholds.
However, RHs should be increasing by then.

&&

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

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

19/69



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