Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 200900

Area Forecast Discussion
National Weather Service Brownsville TX
400 AM CDT Sun Aug 20 2017

.SHORT TERM (Today through Monday):Water vapor satellite imagery
shows 500 mb low pressure spinning over the eastern Gulf of Mexico.
Model guidance progs this system to move gradually west across the
Gulf of Mexico during the short term forecast period, ending up in
the western Gulf of Mexico by sunset Monday evening. This mid-level
low pressure system will nudge 500 mb high pressure north and west
as it advances. Dry weather will prevail today and tonight over the
inland portion of the BRO CWFA, with the only hope for isolated
showers occurring tonight over most of the Lower Texas coastal
waters. On Monday, isolated showers are possible along and east of
the Interstate 69E corridor as the mid-level low approaches and
precipitable water values begin to increase to near 2 inches.
Unfortunately, not enough cloudiness and precipitation will occur
to prevent temperatures from reaching well above normal levels. In
fact, inherited daytime highs and overnight lows were increased by
a degree or two based on observations from the past couple of days.

.LONG TERM (Monday Night through Saturday): First things first,
Harvey has dissipated into an open wave (tropical wave) but
continues to move steadily westward. This wave will continue to be
monitored for regeneration as most global models show the wave
moving into the Bay of Campeche mid to late next week.

There remains a lot of uncertainty on the chance of rain this
week and especially next Friday and Saturday. Initially the large
upper low to is still indicated by GFS,ECMWF, Canadian the GEFS to
drift west across the Gulf but stalling just east of the Texas
coast Wednesday as it bumps into the La Canicula Ridge. The upper
low then is shown to weaken Thursday leaving a weak shear zone
over the Western Gulf going into next weekend. Moisture although
shows some increase it remains limited in depth and content also
with CWA on the west side of the low/shear line upper support for
lift is limited. We would have to depend on the sea breeze and
daytime heating to do the lifting. GFS/EC guidance remains
reluctant to raise pops above 20 percent Tuesday through Thursday
so no change in the previous forecast with slight chances mainly
along and east of I-69C/281. As we move into Friday and
Saturday globals models are in somewhat agreement with a moisture
surge over South Texas as the tropical wave (Harvey remnants)
move into the Southwest Gulf which is reasonable and
climatologicalfavorable for this time of year. As a result, the
rain forecast was left unaltered maintaining chance pops for the
end of next week.

Temperatures to see little variation Tuesday through Thursday from
what has been experienced the last several weeks. With the upper
ridge the dominating feature and the upper low not expected to
move over the region temperatures are likely to remain on the
higher end of guidance. Not until days 6 and 7 would we see a few
degrees drop in highs and lows if the increase in rain chances


.MARINE:(Today through Monday): Buoy 42020 reported southeast winds
around 12 knots gusting to around 14 knots with seas slightly over
2.5 feet with a period of 4 seconds at 02 CDT/07 UTC. Surface high
pressure will produce light to moderate winds and low to moderate
seas for the Lower Texas coastal waters during the period. Small
Craft Exercise Caution and Small Craft Advisory are not likely to
be needed.

Monday night through through Thursday...A weak pressure gradient
is likely to remain across the Western Gulf much of next week with
an upper ridge over Texas and an upper low moving over the Western
Gulf keeping the surface features weak. No tropical issues are
anticipated at this time with Tropical Storm Harvey having
dissipated into a tropical wave. Light to moderate onshore winds
and a slow sea state to persist much of next week.


BAYVIEW/PORT ISABEL  96  80  95  79 /   0   0  20  10
BROWNSVILLE          98  79  96  78 /   0   0  20  10
HARLINGEN            99  78  98  77 /   0   0  20  10
MCALLEN             103  80 101  79 /   0   0   0  10
RIO GRANDE CITY     105  78 102  77 /   0   0   0  10
SOUTH PADRE ISLAND   90  83  92  83 /   0   0  20  10




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