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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 230548 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1248 AM CDT Mon Sep 23 2019

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

.AVIATION...VFR will prevail through the remainder of the
overnight hours with light surface winds. Tomorrow, VFR will
continue as winds become moderate with breezy gusts. Isolated
convection is forecast, but continues to be excluded from the
latest iteration of TAFs. Cloud cover may be more widespread
Monday night such that MVFR may occur with light winds at the

.PREV DISCUSSION... /issued 633 PM CDT Sun Sep 22 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR conditions prevail through the TAF period with
increasing clouds expected into Monday afternoon. Isolated showers
are possible overnight, mainly along the coast. Patchy fog may
develop late tonight, mainly north of the RGV. Thunderstorms and
showers are expected to develop along the sea breeze late Monday 
morning into Monday afternoon with potentially limited coverage 
across the RGV. Any showers that do develop may contain locally
heavy rainfall.

PREV DISCUSSION... /issued 321 PM CDT Sun Sep 22 2019/ 

SHORT TERM (Tonight through Monday Night): Models show a weak 
inverted trough moving west under the main northern Gulf Coast H5
ridge. The energy will be best placed to enhance local convection
Monday and Monday night. With ample low level moisture in the 
area, the Gulf waters and coastal sections will see isolated to 
scattered showers and thunderstorms, with some convection 
penetrating a bit farther inland than recent typical sea breezes 
on Monday, into the mid valley and Hidalgo County. Deeper moisture
coupled with efficient rain processes could result in moderate to
brief heavy rain producers Monday afternoon through evening. 
Skies should be mostly clear to partly cloudy tonight with light 
southeast winds and a bit of patchy fog across the northern 
ranchlands and brush country. Temperatures will trend warmer than 
normal by a few degrees through the short term, with partly cloudy
to mostly cloudy skies Monday and into Monday night.

LONG TERM (Tuesday through Sunday): 500 mb ridging will start off
the longer range period centered over the Gulf of Mex with closed
lows bracketing this ridge to the west and east. A major Baja
closed low will be located over the western U.S./Mexico border
region while a series of 500 mb closed lows/troughs will stretch
from north to south over the western Atlantic. Meanwhile, a
general weakness on the west side of the 500 mb ridging will be
centered over the Deep South TX/RGV region from Tues through Thurs.
This will likely help initiate some isold/sct conv. The one 
limitation for this feature will be that deep layer moisture will 
be pretty limited or will remain concentrated over the western
Gulf. This weakness will get sheared out to the north ahead of the
Desert SW closed low which will open up to a trough and will move
into the TX Panhandle region late Thurs/early Fri. As the 500 mb
weakness lifts out to the north and east, the broad ridging will
build westward into next weekend which will maintain overall temps
above climo for the end of Sept. 

The ECMWF temps have been consistently warmer versus the GFS as 
the ECMWF appears to bring in a little drier air over the region 
until around Thurs. Model blends for high temps appear to lean 
towards the warmer ECMWF numbers throughout the upcoming work week
and this looks reasonable. The ECMWF and GFS are also in 
reasonable agreement for pops through Day 7/8 and will maintain 
the conv chcs generally in the 20 to 30 % range for the inland and
marine regions through next weekend. 

The tropical Atlantic Basin remains active today with NHC
monitoring TS Jerry and Karen in addition to a broad area of low
pressure emerging off of the west coast of Africa. TS Jerry is
expected to recurve to the N and NE moving into the northern
Atlantic Thur and Fri. Meanwhile, TS Karen is expected to 
continue moving in a general northerly direction moving north of 
Puerto Rico on Thurs and Fri. At this point longer range model 
guidance indicates that the 500 mb ridging building over the SE 
U.S. may cause Karen to slow down and possibly stall. Please refer
to the latest outlooks and statements from NHC concerning the 
future progress of TS Karen. 

MARINE Now through Monday night: Light to moderate southeast
winds and moderate seas will prevail in the short term. A mid 
level inverted trough will approach from the east tonight and 
Monday, contributing to instability aloft and supplementing moist 
low level inflow from the southeast, with isolated to scattered 
convection in the forecast for the marine areas. Seas should dial 
back slightly tonight through Monday night, though low end small 
craft should exercise caution conditions may still develop at 
times, especially offshore.

Tuesday through Thurs Night: Broad surface ridging over the Gulf
of Mex and the SE U.S. will maintain a pretty moderate and steady
SE low level flow across the Laguna Madre and the lower TX Gulf
waters through Thurs. Gulf swells will likely remain in the 2 to
4/3 to 5 foot range through Thurs. This will keep the Bay and Gulf
conditions under SCA levels, but some periodic SCEC conditions
cannot be ruled out. Isold/Sct conv will remain possible
especially across the lower TX Gulf waters due to decent and
persistent maritime CAPE values. 



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