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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 201123 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
623 AM CDT Sun May 20 2018

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

.AVIATION...Unanticipated light showers moved over the BRO and HRL
aerodromes over the past hour, but all convection has now either
dissipated or moved away. No additional rainfall is expected
during the TAF period. MVFR right now will give way to VFR after
sunrise, with a slip back into MVFR beginning around sunset this

.PREV DISCUSSION... /issued 325 AM CDT Sun May 20 2018/ 

SHORT TERM (Now through Monday): KBRO Doppler radar currently shows
very isolated showers and thunderstorms over the BRO CWFA and 
over neighboring Mexico right now. Unfortunately, this activity 
should be gone by sunrise this morning, with dry conditions on tap
for the rest of today. Tonight, another round of very isolated 
convection may occur as it once again transitions from Mexico to 
Deep South Texas and the Rio Grande Valley. A 500 mb ridge of high
pressure building north over the Lone Star State should return 
the dry weather for Monday. Continued above normal daytime high 
and overnight low temperatures are also expected to continue. 

LONG TERM (Monday night through Saturday): A 500 mb low will
begin to open and lift northeastward across the Four Corners
region early next week. A couple of weak shortwave troughs will 
move out ahead of the main trough through Central Texas Monday 
night into Tuesday, but ridging will likely dominate across Deep 
South Texas as the main energy stays well to the north. Rain
chances will be very low each day for the upcoming week and will
be dependent on any sea breeze development. The pressure gradient
at the surface will weaken around mid-week with winds out of the
ESE at 5 to 10 knots, so there will be a better chance of sea 
breeze development, but there may not be enough moisture for much
precipitation. Therefore, have kept PoPs at 5 to 10% across the

For the second half of the week, the mid-level ridge of high 
pressure will shift westward over Mexico with northwest flow and 
strong subsidence across South Texas. Near-zero rain chances and 
hot temperatures will continue into the weekend. Model guidance
indicates highs in the mid 90s in the Lower RGV to upper 90s in
the Upper RGV by the end of the week and possibly higher. Towards
the end of the long term, several locations may exceed the century
mark with 850 mb temperatures ranging from 22 to 25 C and 1000-500
mb thicknesses of 580 dam all the way to the Gulf coast.

MARINE (Now through Monday): Buoy 42020 reported east-southeast 
winds around 16 knots gusting to around 19 knots with seas slightly 
over 5 feet with a period of 7 seconds at 250 CDT/750 UTC. The 
surface pressure gradient is expected to relax slightly during the 
forecast period, allowing for a slight diminishing of winds and 
subsidence of seas. Although Small Craft Advisory is not expected to 
be needed along the Lower Texas Coast, Small Craft Exercise Caution 
will likely be needed for the Laguna Madre and Gulf of Mexico 
waters, especially today and/or tonight. 

Monday night through Friday: The pressure gradient across the
Western Gulf of Mexico will weaken some next week allowing the 
winds and seas to remain fairly low. ESE to SE winds will range
from 10 to 15 knots with seas gradually subsiding to 2 to 4 feet.



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