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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

FXUS64 KBRO 191740 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1240 PM CDT Mon Aug 19 2019

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

.AVIATION...Satellite and radar images as well as surface 
observations indicate a little more cumulus development today 
compared to yesterday with some hints of convection developing 
along the seabreeze front moving inland across the lower Texas
coast early this afternoon. Ceilings were near 4800ft at KEBG to
near 5500ft at KBKS. Expect VFR conditions to prevail across the
Rio Grande Valley through the rest of the afternoon into the early
evening as the 500mb subtropical ridge across the state continues
to provide subsidence across southwest Texas. 

.PREV DISCUSSION... /issued 630 AM CDT Mon Aug 19 2019/ 
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR conditions expected to prevail through the TAF
period with high pressure in full control. As previously
advertised, a few brief periods of MVFR CIGs are possible from 
the southeast as streamer clouds work inland from the Gulf this 
morning and again late tonight. Southeast winds once again gust to
20-24 kts this afternoon, although, not as breezy as the weekend.

PREV DISCUSSION... /issued 341 AM CDT Mon Aug 19 2019/ 

SHORT TERM (Now through Tuesday): High pressure heads northwest 
through the short term period, allowing the pressure gradient to 
weaken, and letting southeasterly winds generally decrease, across 
Deep South Texas today and tomorrow. Wind gusts this afternoon 
should still reach 20-25 mph at times, especially across the mid to 
lower Rio Grande Valley. An isolated shower or thunderstorm is 
possible along the seabreeze, mainly across Willacy or Kenedy 
counties, this afternoon, otherwise, dry conditions will persist 
through Monday night. 

With high pressure edging northwestward, the seabreeze on Tuesday, 
and likely into the long term, may be able to march further inland, 
possibly tapping into the heat to initiate shower or thunderstorm 
development. Have bumped silent POPs on Tuesday afternoon a nudge, 
still staying below 15 percent, but expecting some sort of life out 
of the seabreeze advancing west. Expect an increase in clouds across 
the coastal counties, at the very least, today into Tuesday. 

Have decided to once again issue a Heat Advisory across the central-
east counties, with the highest Heat Indices expected along and east 
of I69C to along and mostly west of I69E. This may be the last gasp 
of the recent heat wave in regards to heat headlines, as Heat 
Indices for Tuesday reside below any Heat Advisory criteria at this 
time, generally peaking at 105 to 109 degrees. Will hold off on 
issuing a Rangeland Fire Discussion today, as conditions appear to 
be just below criteria. A fire weather discussion will continue 

LONG TERM (Tuesday Night through Sunday): The long term period will 
begin with an inverted trough nudging into deep South Texas, pushing 
the 500 mb ridge further north into the Southern Plains and Four 
Corners region. The weakness in 500 mb heights along with low to mid 
level moisture advection will bring increased cloud cover and PoPs 
into our CWA. As such, high temperatures are expected to drop 
slightly (although still likely stay above normal) and bring a 
little respite from the oppressive heat. Best chance of showers and 
thunderstorms will be along the coastal areas and offshore where 
models keep the majority of the moisture.

On Thursday, models show a 500 mb low form in the western Gulf and 
begin tracking northward around the northwestern edge of the Gulf 
through Saturday. While this feature is shown on both the ECMWF and 
GFS, discrepancies in its development bring down forecast confidence 
a bit through the rest of the forecast period. The ECMWF has a 
closed 500 mb low skirt along the northwestern Gulf on Friday and 
keeps the bulk of the low to mid level moisture offshore. However, 
the GFS shows this feature to be less organized and brings the 
moisture further inland across our CWA as it makes its trek along 
the northwestern Gulf. Regardless of the discrepancies between the 
models, both are in agreement with the increased moisture mostly 
over our coastal region and Gulf waters, so have kept a slight 
chance of showers and thunderstorms through the period with the best 
chances being offshore. 

The forecast for Sunday will depend primarily on the development
and progression of a mid level trough. With widely varying model 
solutions this far out, will go with a slight chance of showers 
and thunderstorms for now.

MARINE (Now through Tuesday): High pressure edges northwest toward 
the Desert SW over the next couple of days, weakening the pressure 
gradient across the lower Texas coast. This will allow the southeast 
onshore flow to also decrease into Tuesday. Afternoon wind gusts may 
still reach 20 knots this afternoon across the Laguna Madre and 
nearshore Gulf of Mexico waters. Small craft should exercise caution 
this afternoon and early evening. Gulf seas eventually subside as 
wind speeds overall decrease through Tuesday, with 3-5 feet expected 
today, shifting further offshore and generally subsiding to 2-4 feet 
Tuesday, and 2-3 feet with improving surf conditions along the lower 
Texas coastal shoreline. 

Tuesday Night through Friday...Light to moderate southeast winds
will continue across the coastal waters on Tuesday night with
surface high pressure across the eastern Gulf of Mexico. The
pressure gradient will begin to weaken by midweek and allow winds
to diminish on Wednesday, but then pick up again heading into
Friday with a tightening of the pressure gradient. Seas generally
follow the wind pattern trending 2 to 4 or 2 to 3 feet through
Thursday and then building to 3 to 5 feet on Friday. Showers and
thunderstorms will be possible at times across the coastal waters
throughout the period.

FIRE WEATHER...Rangeland Fire Discussion may not be needed today as 
conditions appear to stay just below criteria. Humidity values this 
afternoon are expected to be slightly higher than observed yesterday 
across the western counties, with 20 foot wind speeds generally 
staying below 15 mph or higher until later this afternoon or early 
this evening, as the lowest humidity values have already rebounded. 
Still, humidity values in the mid to upper 20 percent range are 
expected across Zapata, Jim Hogg, and Starr counties with breezy 
southeast winds. Couple those conditions with critically dry fuels 
across most of Deep South Texas, and burning of any kind, west of 
I69C especially, should be strongly discouraged and postponed a 
couple of days. At this time, drier air is expected out west on 
Tuesday, with humidity values dipping into the low to mid 20 percent 
range and 20 foot wind speeds again near 15 mph, mainly later in the 

TX...Heat Advisory until 6 PM CDT this evening for TXZ250-251-253>255-



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