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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 200522 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1222 AM CDT Tue Aug 20 2019

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


.AVIATION...VFR conditions prevail through the TAF period, aside
from brief periods of MVFR CIGs due to streamer clouds from the
southeast off the Gulf of Mexico. Like last night, most reductions
should be short lived. Southeast winds continue and once again become
breezy this afternoon, possibly turning more easterly with the
seabreeze by mid afternoon. Confidence is low on any precip, but
slightly better chance of a shower toward BRO this morning with a
passing streamer shower. A shower or thunderstorm may develop
along the seabreeze this afternoon, likely north of the valley,
and very isolated. 


.PREV DISCUSSION... /issued 641 PM CDT Mon Aug 19 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR expected to predominate at the RGV terminals over
the next 24 hours. Can't rule out brief periods of higher MVFR
ceilings at any of the airports overnight, per obs from last night
and RAP/BUFKIT forecast soundings. Ceilings, if any, should be
very brief. Breezy SE winds will subside after sunset, with 
somewhat lower daytime winds speeds expected on Tuesday vs. today.
A wind-shift to ESE with the sea-breeze boundary is expected mid-
afternoon. An isolated, brief streamer shower passing over BRO 
early in the morning can't be ruled out, but should cause little-
to-no impact.

PREV DISCUSSION... /issued 253 PM CDT Mon Aug 19 2019/ 

SHORT TERM (Now through Tuesday night): Heat index values are 
currently near 115 degrees in Brownsville while heat index values 
range from 105 to to 110 degrees across the eastern portions of the 
CWA this afternoon. Will continue current heat advisory in effect as 
temperatures will remain hot the rest of the afternoon into the 
early evening and dewpoint temperatures remain in the lower to mid 
70s across Cameron and Hidalgo counties. The only relief to the heat 
today was the brief showers that developed along the seabreeze front 
across the coastal counties. Unfortunately...Brownsville did not see 
any relief to the heat as the record high temperature of 100 degrees 
was tied today...previously set in 1915. 

GOES-16 total precipitable water value satellite images are at least 
encouraging as they indicate PW values near 2 inches across the 
northwest Gulf of Mexico and the coastal sections of Texas this 
afternoon. With the isolated showers that developed across the 
coastal counties least the potential exists for 
additional seabreeze convection Tues afternoon. At the very 
least...the increase in cloud cover Tuesday will provide some 
respite to the heat but it will still remain hot. Currently not 
expecting heat advisory conditions for tomorrow and record high 
temperatures but it will still be hot as the 500mb subtropical ridge 
across south-central United States continues to provide strong 
subsidence across western portions of south Texas. 

LONG TERM (Wednesday through Monday): An inverted trough will 
approach deep South Texas while pushing the prevailing 500 mb ridge 
further north into the Southern Plains and Four Corners region on 
Wednesday. This mid level feature will allow deeper moisture to 
increase across the region mid to late week. The best rain chances 
are expected to remain across the eastern portions of the CWA and 
over the Gulf waters Wednesday through Friday. The increase in cloud 
cover and rain chances should keep high temperatures a bit lower 
through mid to late week. 

The rest of the forecast period is dependent on the development of a 
closed 500mb low across the northwest Gulf of Mexico by late in the 
week. The ECMWF continues to indicate that this feature will move 
along the northwestern Gulf of Mexico on Friday with most of the 
moisture remaining offshore with subsidence across the CWA. While, 
the GFS shows a weaker and wetter system moving west across the 
northwestern Gulf. No significant changes were made to the previous 
pop and temperature grids. Will keep the mention of a slight chance 
to chance of showers and thunderstorms across the CWA through the 
weekend into early next week.

MARINE (Now through Tuesday night): Seas were near 4.3 feet with 
south to southeast winds near 9.7 knots at buoy020 early this 
afternoon. Light to moderate southeast winds winds will prevail 
across the coastal waters tonight with weak surface high pressure 
across the Gulf of Mexico. The pressure gradient will weaken across 
the lower Texas coast Tuesday. Light southeast winds will prevail 
across the western Gulf of Mexico Tuesday with slightly higher winds 
across the Laguna Madre Tues afternoon. Winds will increase slightly 
across the offshore waters Tues night as the winds decouple across 
the bay waters. 

Wednesday through Saturday...Light to moderate southeast winds 
and low to moderate seas will prevail Wednesday through Friday 
night. Showers and thunderstorms will be possible at times across 
the coastal waters through the period.

FIRE WEATHER...Relative humidity values have fallen below 35 
percent across the western portions of the CWA this afternoon as 
winds have increased to 15 to 20 mph with gusts to 25 mph. With 
critically dry fuels across most of deep south Texas...have issued a 
fire danger statement for the CWA except across the coastal counties 
for this afternoon. RH values are expected to be slightly lower 
across the western portions of the CWA Tues afternoon and 20 foot 
winds are expected to be similar to today so a fire danger statement 
will likely be needed again tomorrow. 




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