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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 210515 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1215 AM CDT Sat Sep 21 2019

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

.AVIATION...VFR will be the rule through the next 24 hours. Breezy
winds are anticipated for the daylight hours of Saturday. Isolated
convection will occur, but will not be widespread enough to warrant
inclusion in the TAFs. 

.PREV DISCUSSION... /issued 632 PM CDT Fri Sep 20 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR conditions expected to prevail through the TAF
period, with low level clouds streaming northwestward tonight into
Saturday. An isolated shower is possible off the Gulf of Mexico
overnight, with brief MVFR CIGs, mainly toward BRO and HRL. 
Southeasterly winds become breezy again on Saturday, generally
lighter than today as high pressure weakens. An isolated 
thunderstorm is possible late Saturday morning into the 
afternoon, mainly along the coastal counties with the sea breeze.

PREV DISCUSSION... /issued 400 PM CDT Fri Sep 20 2019/ 

SHORT TERM (Now through Saturday Night): GFS and ECMWF continue 
to show a weak mid-level disturbance approaching the Lower Texas 
coast Saturday. Current water vapor imagery are having a difficult
time detecting this shortwave and with the mid level high 
pressure building westward over Texas would expect this 
disturbance to dampen out a bit more as it approaches the coastal 
regions tomorrow. Model guidance show a moderate spread in pops 
ranging from 10 to 35 percent maintaining confidence of low grade 
pops for Saturday afternoon. The disturbance to combine with the 
sea breeze, which might have a bit more oomph with a weakening 
pressure gradient, to trigger the late morning/afternoon 
convection. Best probabilities will be within the I 69E and C 
corridors. Given atmospheric moisture content remains moderately 
high with pwats around 2 inches a brief downpour is possible. 

Otherwise, any remaining very isolated convection today should quick 
wane by or shortly after sunset with skies becoming clear until the 
early morning hours when patchy stratus forms over portions of the 
North and West Ranch lands. Temperatures remain elevated in the mid 
to upper 70s tonight with southerly breezes slowly decoupling. Highs 
Saturday very similar to the last few days topping out in the mid to 
upper 90s most areas and area out west reaching the century mark. 
Heat indices may be a degree or two higher with a slight bump in dew 
points or less afternoon mixing. Saturday night will see lower winds 
and mostly clear skies which allows temps to drop into the mid

LONG TERM (Sunday through Friday): A stout 593-594dam 500mb 
ridge, centered over the southeastern US, will keep conditions 
abnormally warm and mostly dry across Deep South Texas on Sunday.
There should be enough boundary layer moisture for a few isolated
showers and thunderstorms during the daytime, especially along and
east of the US 281 corridor. As stated in the previous forecast
discussion, both the GFS/ECMWF continue to show a weak inverted
mid-level trough that moves over the area Monday morning and
afternoon. Mid-range forecast models are producing PWAT values 
between 2.00-2.25 inches between Monday morning and Monday 
evening. Kept PoPs around 30-40%, lower across the western CWA, 
through Monday evening.

Forecast models continue to agree that mid-level riding will
weaken after Monday, with Deep South Texas becoming sandwiched
between a synoptic trough to the northwest and ridging to the 
east by the end of the upcoming week. Isolated sea breeze 
convection will be possible each afternoon between Tuesday and the
end of the long-term period, with coastal counties having the 
best opportunities for precipitation.

Temperatures are expected to remain abnormally warm through the
upcoming week. Afternoon highs are expected to be about 5-10
degrees above seasonal normal, ranging in the lower-upper 90s, 
and even lower 100s out west. Overnight low temperatures will 
also continue to be abnormally warm, with lows in the mid-upper 
70s each night.

MARINE (Now through Saturday Night):  Pressure gradient across the 
Western Gulf of Mexico begins to weaken tonight into Saturday with 
the remnants of Imelda dissipated and surface high pressure over the 
Southeast U.S. weakening. Slightly elevated winds and seas are 
expected through tonight mainly over the Gulf waters with moderate 
onshore flow Saturday and light to moderate winds Saturday night. 
Seas respond with the wind waves slowly subsiding later tonight 
becoming slight to moderate Saturday. An isolated shower or 
thunderstorm is possible anytime with the best shot for the Laguna 
around sunrise through Saturday morning.

Sunday through Friday: Weak high pressure over the Gulf will 
result in a weak surface pressure gradient, with light to modest 
south to southeasterly breezes. Anticipate for seas to continue to
be generally around 2 to 5 feet. Winds and seas could approach 
small craft exercise caution levels at times but no advisory 
conditions will be expected. Isolated to scattered marine showers 
and thunderstorms will remain possible through the period.



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