Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 221037 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
537 AM CDT Tue Aug 22 2017

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

.AVIATION...VFR will be the rule through the next 24 hours.
Isolated convection remains anticipated today and will remain
excluded from the forthcoming TAFs. Surface winds will increase
and back as the seabreeze front progresses westward before
becoming light and variable overnight tonight.

.PREV DISCUSSION... /issued 407 AM CDT Tue Aug 22 2017/

SHORT TERM (Today through Wednesday):The KBRO upper air sounding
from Monday evening showed a precipitable water content of 1.93
inches in the atmospheric column, an increase of .26 inches from
Sunday evening. This deeper tropical moisture is expected to persist
near its current level throughout the forecast period as an inverted
500 mb trough (seen on water vapor satellite imagery spinning just
south of central Louisiana) lingers over the western Gulf of Mexico.
Isolated showers and thunderstorms will affect the central and
eastern portions of the BRO CWFA and the adjacent coastal waters
today through Wednesday. The slightly increased cloud cover and
isolated precipitation chances may help to hold temperatures at
near normal levels for a change.

LONG TERM (Wednesday Night through Monday): To say the least the
long term forecast continues to have large uncertainty with the
remnants of Harvey remaining disorganized with no organization or
change to the convection pattern from 24 hours ago. From what
satellite and current observations indicate is the tropical wave
axis in along the Eastern Yucatan with convection quite wide
spread from just south of Cuba to the Northeastern Yucatan.
Main difference overnight is the latest model output which is not
as tightly clustered as yesterday. Deterministic global,
hurricane and ensemble models have trended with a broader track
guidance with the mean track favoring a slight turn to the right
or farther east and north of the Lower Texas Coast. Not all the
model track on this trend with still some to the south of region
which keep the going forecast trends in play for at least this
forecast package.

Broad mid to upper level troughiness to dominate the Western Gulf
which is combination of the weakening upper low over the Central
gulf and combination of the tropical wave emerging off the
Yucatan. The RGV will be on the western side of this trough so
will maintain slight chance for seabreeze activity. As everything
tries to congeal into some type of tropical cyclone Wednesday
night through Friday and beyond one would expect rain chances to
increase along with some wind and of course Marine weather
concerns. Forecast plays up all these elements but is very
conservative due to the high uncertainty. All Interest in the RGV
and Lower Texas coastal reaches shouldn`t focus too much exact
details yet, but confidence continues to increasing for some kind
of impacts to the RGV/Deep S. TX later this week. The main impact
at this time remains rain with a large surge of tropical moisture
still indicated to overspread the region later Thursday through
Saturday. WPC has placed the eastern half of the CWA in an
Excessive Rainfall outlook on Day 3 (12Z Thu-12Z Fri) with the
bulk of tropical moisture expected after 12Z Friday. In any
case...pops remain high (50-70 percent) Thu night-Saturday before
some tapering takes place Sat night-Monday. Temperatures will
take a plunge Friday and Saturday with the increased cloud cover
and rain chances however humidity levels are likely to be
impressive with dew points remaining near 80 degrees near the
coast making the region very uncomfortable. It remains to early to
talk winds and storm surge detail with no storm to track at this

MARINE:(Today through Wednesday): Buoy 42020 reported east winds
around 8 knots with seas slightly over 3.5 feet with a period of 5
seconds at 02 CDT/07 UTC. Light to moderate winds and low to
moderate seas will continue to be the rule along the Lower Texas
Coast with surface high pressure in control over the western Gulf of
Mexico. Small Craft Exercise Caution and Small Craft Advisory are
not likely to be needed.

Wednesday night through Sunday: Mariners and recreational
fisherman need to pay close attention to the latest forecast the
next several days. Models continue to indicate the potential for
some type of tropical cyclone to form in the Bay of Campeche
Wednesday and move steadily Northwest. Forecast remains highly
uncertain on exact track and strength of this system as models
continue to trend with its forecast track to move over, very near
or just northeast of the Lower Texas coast Friday. Confidence
remains highs for some impacts for higher seas, winds and
widespread heavy showers/thunderstorms Thursday night through
Saturday and may even linger into Sunday.



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