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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 171150 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
650 AM CDT Sun Jun 17 2018

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


.AVIATION...Light winds and a few passing clouds prevail across 
deep south Texas this morning. Showers will develop along the 
coast this morning as a surface trough and an upper level low 
across the southern Gulf of Mexico moves westward across the 
western Gulf of Mexico today. Showers and thunderstorms will 
develop across the eastern portions of deep south Texas this 
afternoon as tropical moisture continues to increase across the 
lower Texas coast. Expect VFR conditions for the next 24 hours. 
However, brief MVFR conditions will be possible in the vicinity of
convection at local aerodromes this afternoon. 


.PREV DISCUSSION... /issued 410 AM CDT Sun Jun 17 2018/ 

SHORT TERM (Today through Monday): Brownsville radar indicates 
some isolated activity over the Gulf waters this morning. Latest 
GOES-16 Total Precipitable Water imager shows precipitable water 
values of 1.8 to 2.1 inches across deep south Texas. Water vapor 
satellite imagery currently shows a fairly dry airmass in place 
over much of the region with a large plume of moisture over the 
western Gulf of Mexico. Moisture aloft will steadily increase 
through the short term as the mid to upper level low over the 
southwest Gulf of Mexico moves westward across the western Gulf of
Mexico today.

The combination of a surface trough and an approaching 500mb low, 
will allow deep tropical moisture to surge into the eastern portions 
of the CWA by late this afternoon. Scattered showers and 
thunderstorms are expected to develop across the area today with the 
best rain chances near the coast. Showers and thunderstorms are 
expected diminish after sunset with convection redeveloping 
overnight over the Gulf waters. Scattered to numerous showers and 
thunderstorms are expected on Monday, the potential for heavy 
rainfall will be possible, generally along and east of the I-69C/US 
281 corridor, on Monday. Temperatures are expected to be near or 
slightly above normal levels through the period due to increasing 
clouds and robust rain chances. 

LONG TERM (Monday Night through Saturday): The upper trough and
associated surface tropical wave will be nearly directly overhead
by early Tuesday, keeping the moisture flow going across the area.
Models continue to show PW values well above 2 inches continuing
into Wednesday, which means any precipitation that develops will
be efficient and abundant rain producers. Overall rainfall
accumulation of 3 to 6 inches is becoming more likely with each
successive model run. Main moisture tap shift away from the region
later in the week, but PW values noted between 1.7 and 1.9 still
means that precipitation will still be a possibility each day, 
with locally heavy downpours continuing. 

MARINE: Now through Monday: Buoy 42020 reported southeast winds 
around 14 knots gusting to around 16 knots with seas slightly 
under 4.6 feet with a period of 7 seconds at 0330 CDT/0830 UTC. 
Light to moderate onshore flow will continue through Monday with 
surface high pressure over the northeastern Gulf of Mexico. 
Adverse marine conditions will gradually develop on the Gulf 
waters through the period as swells continue to build from a 
strengthening southeasterly fetch across the western Gulf. 
Increasing moisture will support scattered to numerous showers and
thunderstorms along the lower Texas coast through the period. A 
Small Craft Advisory will likely be needed for all or portions of 
the Gulf waters by tonight due to increasing swells. 

Tuesday through Thursday: weak surface troughing along the coast
will continue to produce modest southeast flow across the region,
generally 10 to 15 knots each day. Some models try to strengthen
the low Wednesday across Deep South Texas, which would provide
higher winds, but this seems overly aggressive compared to the
remainder of models. There is expected to be a considerable fetch
across the Gulf, which will keep seas 6 to 7 feet offshore the 
entire period. Small Craft Advisories will likely be ongoing, and
will continue into the latter half of the week.




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