Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 201141 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
641 AM CDT Thu Jul 20 2017

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

.AVIATION...Very few changes were needed to the previous set
of TAFs. VFR is expected through the next 24 hours with high
pressure at the surface and in the middle layers of the
atmosphere dominating over Deep South Texas and the Rio Grande
Valley. Any convection that develops will be very isolated and
is not included in the current TAFs for that reason.

.PREV DISCUSSION... /issued 357 AM CDT Thu Jul 20 2017/

SHORT TERM (Now through Friday): The KBRO upper air sounding from
Wednesday evening showed a precipitable water content of 1.86 inches
in the atmospheric column. Enough deep moisture should remain within
Deep South Texas and the Rio Grande Valley to generate isolated
convection along and east of the Interstate 69C/Highway 281 corridor
today, with streamer activity over the adjacent coastal waters and
the coastal portions of Cameron, Willacy, and Kenedy Counties
tonight. A drier atmosphere on Friday will lead to dry weather for
the entire BRO CWFA. Inherited daytime high and overnight low
temperatures appeared too cool given recent trends and were raised
to well above normal levels for the short term forecast period.

LONG TERM (Friday Night through Wednesday): The beginning of the
long term will include mainly hot and dry conditions as abundant
dry air moves into Deep South Texas through the weekend. The
synoptic pattern consists of broad mid-level high pressure
shifting to the east coast with weakening low pressure
retrograding westward into the upper Texas coast. Don`t expect
much in the way of rainfall as RH values will range from 30 to
50% above 850mb amid strong subsidence. At the surface, high
pressure over the northeast Gulf will maintain breezy southeast
winds Saturday and Sunday along with increasing heat and elevated
dew points. Heat Indices may reach 110F at times in the mid to
upper Rio Grande Valley.

Next week, models indicate a surge of deeper moisture moving in
off the Gulf as a weak inverted trough/low pressure develops. The
GFS is showing the more rigorous and wetter solution while the
ECMWF keeps most of the moisture well to the south going into
central Mexico. Have decided to keep mainly slight chance PoPs for
Tuesday and Wednesday. Temperatures will depend on how much cloud
cover and precipitation we see, but highs at this points should
be around normal to slightly below normal for late July.

MARINE (Now through Friday): Buoy 42020 reported south winds around
16 knots gusting to around 18 knots with seas slightly over 2.5 feet
with a period of 4 seconds at 03 CDT/08 UTC. High pressure centered
over the north-central Gulf of Mexico will continue to 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 will not be needed.

Friday night through Wednesday: Moderate southeast flow will
persist through much of the long term period as surface high
pressure persists over the northeast Gulf. Winds may be gusty at
times, approaching Small Craft Exercise Caution conditions
Saturday night through Monday night as low pressure develops in
the Plains. Seas will eventually build to 4 to 6 feet across the
offshore Gulf waters for the first half of next week.



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