Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 190515
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
1215 AM CDT Mon Jun 19 2017

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

&&

.AVIATION...Dissemination issue with the NWS Gateway has made
NUMEROUS surface observations unavailable across the entire
country for approximately three hours now. However, satellite
imagery is showing that VFR conditions are prevailing across Deep
South TX at this time. As the lowest layers of the atmosphere cool
overnight, am expecting SCT to BKN cumulus to develop across the
region between 09Z to 13Z this morning from roughly 2K to 2.5K
feet in line with the strong inversion evident in the KBRO 6/19
00Z upper air sounding. Cumulus to diminish through the mid to
late morning hours due to daytime heating with VFR conditions
prevailing once again through the remainder of the TAF period. Not
as breezy today compared to Sunday with afternoon winds only
gusting to around 18 knots at most. Winds to diminish around
sunset and after.

&&

.PREV DISCUSSION... /issued 644 PM CDT Sun Jun 18 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...CU field remains confined to the immediate coast, and
is remaining SCT. Cu should dissipate in the next couple hours
with loss of daytime heating. Winds will also decrease to around
10 knots areawide. Lower clouds are possible again later tonight
across the inland regions, especially around KMFE. Overnight
clouds dissipate quickly tomorrow morning, with daytime CU
gradually developing and rising to 4000 feet by noon. Temperatures
tomorrow will again reach near 100 degrees areawide, with heat
index values of 105 to 110.

PREV DISCUSSION... /issued 244 PM CDT Sun Jun 18 2017/

SHORT TERM (Now through Monday night): The large, stationary ridge
over Northwest Mexico and the Southwest United States will reorient
to the north as a mid level trough digs into the upper Midwest and
the Great Lakes region. The result will be a continued stabilizing
effect over the CWA with the ridge extending into North Texas, but
with upper winds shifting to northeast rather than northwest. Strong
southeast winds over the Gulf and deep South Texas will diminish as
the influence of high pressure over the Gulf is weakened. Winds will
shift more to east on Monday under a mix of tropical clouds and sun
but conditions should continue rainless. Partly cloudy skies and a
shift to easterly winds could produce very slightly cooler weather,
though heat index values on Monday are still forecast to be in the
103 to 108 degree range in the afternoon. Overnight lows will still
be in the mid to upper 70 degree range. Slightly higher relative
humidity values out west and weaker winds will put the kibosh on any
short term fire weather concerns.

LONG TERM (Tuesday through Sunday):The extended period, especially
days Wednesday-Friday, will be highly contingent on future
development and track of the tropical disturbance currently in the
Western Caribbean. The latest 12Z model package are beginning to
trend farther west but there remains a large degree of spread in
the latest solutions. Things to consider are the disturbance
itself has an ill-defined center, just east of the Yucatan
Peninsula and any development will continue to be gradual as it
moves slowly northward into the Southern Gulf Monday and Tuesday.
Others factors are the large dominate mid level ridge over the
Desert SW extending east into Texas, the mid/upper level trough
extending into the Southern Gulf States and the Bermuda High
anchored over the Mid-Atlantic Ocean expected to extend west into
the Southeast States mid-to late next week. With the overall
consensus continuing to trend farther west and unclear consensus
on how the upper trough and the two ridges will influence the
future movement of this system all interests across the Lower
Texas Coast will need to monitor future forecast. With this said
this disturbance will likely be influenced by the trough or the
weakness between the two dominate ridges and move in a northwest
to north direction the next few days then might trend on a
slightly more westward track when and if the upper trough lifts
northeast.

The operational 12Z GFS is beginning to trend more to the left,
or west, and really slows down the forward motion of this
disturbance as it nears the SE Louisiana coast Tuesday or Tuesday
night. It takes another 48 hours (Thursday)for the disturbances to
move inland across SE LA. This is probably due to the mid level
trough lifting northeast, thus the storm runs into weak steering
currents before the Bermuda high builds west and the steering flow
strengthens from the south along the western periphery of the
ridge. The 12Z Canadian is much farther west and is now showing a
1001mb center approaching the Texas Coastal Bend before making a
sharp northward turn Thursday. The greater westward track with the
Canadian is due its indicating a stronger Bermuda high building
well into the Southeast U.S. and the Eastern Gulf. The ECMWF is
the farther west and shows no influence from the upper trough and
takes the weak center to the south of SPI Wednesday before
retreating north parallel to the Lower Texas Coast Thursday and
Friday.

The bottom line up front: it is still way to early to take any model
literally and with to much uncertainty and unknowns will be very
wary to make any big changes to the forecast. Again interest along
the Lower Texas coast, especially the Gulf marine areas, will have
to monitor carefully for any strengthening and westward track of
this system with very low probability of Tropical storm conditions
as early as Wednesday or as late as Friday.

As for sensible weather inland...not very confident on any of the
models but with the models continuing to trend higher on pops even
with the majority of the region on the western dry side of the
system. Will begin to lower pops from west to east and show a
warming trend, yes it can get hotter, as a drier north to northwest
mid level flow will likely to dry out our atmosphere even more.

MARINE:(Now through Monday night): A small craft advisory is posted
for the remainder of the aftn for all waters. Obs suggest a downward
trend in winds and seas and thus do not expect further continuation
of the advisory into tonight. Winds will shift to east Mon and Mon
night as the role of Gulf high pressure weakens. A mid level trough
will move toward the Eastern United States, eroding the influence of
the Bermuda Ridge and the extension of surface high pressure into
the Gulf, along with the approach of weak high pressure into North
Texas to weaken the local pressure gradient, and due to the possible
emergence of a low pressure area from the Western Caribbean into the
South Central Gulf. These themes will result in a relatively quiet
short term period for marine areas.

Tuesday through Friday...There remains a lot of uncertainty with
the future track and strengthening of the the tropical disturbance
in the Western Caribbean. Models continue to indicate a lot of
discrepancy and large spread even through a more westward trend is
indicated by the morning model solutions. All marine interest
along the Lower Texas coast need to monitor future forecast and
discussions for any tropical development and affects of this
system as early as Wednesday and continuing through Friday. Main
impacts if a tropical cyclone does develop will likely be higher
seas/swells and an outside chance of tropical storm conditions.
Wednesday and Thursday and possibly linger into Friday.

&&

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

$$

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19/69



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