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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 182003

Area Forecast Discussion
National Weather Service Brownsville TX
303 PM CDT Tue Jun 18 2019

.SHORT TERM (Now through Wednesday Night):  There will not be much 
change to the ongoing forecast this cycle. Hot and humid weather 
with above normal temperatures (by a few to several degrees above 
normal) will prevail as modest mid level ridging persists over 
northern Mexico and surface high pressure persists over the Gulf of 
Mexico. This will support light to moderate southeast winds under a 
mix of clouds and sun. Limited low level moisture will move up from 
the southwest Gulf and local conditions will remain essentially rain 

Warm and muggy weather under mostly clear to partly cloudy skies 
will prevail tonight and Wednesday night, with low temperatures 
being propped up in part by elevated dew points. Low temperatures 
will range from the middle 70s across the interior brush country and 
ranchlands to the lower 80s in many other locations. On Wednesday, 
morning low clouds will burn off, with the prospect of triple digit 
heat for most inland areas. Moderate southeast breezes will prevail, 
though it could become a little breezier Wednesday afternoon and 
Wednesday night, with strong high pressure over the coastal areas 
combining with lower pressure inland. Along the coast, highs in the 
90s will prevail with upper 80s at the beaches. The above normal 
temperatures and the associated enhanced dew points will support 
lofty heat index values above 110 degrees for a few hours Wednesday 
afternoon, and a heat advisory may be dictated.

.LONG TERM (Thursday through Tuesday): Hot, humid, and breezy-to-
windy weather is expected to continue through early next work-
week. The pattern will be dominated by mid/upper-level subtropical
ridging across much of northern Mexico and extending eastward
across the Gulf. Although the center of the subtropical high gets
displaced a bit from time-to-time, as troughs round its
western/northern periphery, we never really lose its influence.
Heat Advisories appear to be likely each day from Thursday through
Sunday, with some areas (e. g., western Hidalgo, Starr, and Zapata
counties) possibly pushing Excessive Heat Warning criterion
Saturday and Sunday. It will still be hot next Monday and Tuesday,
but a little less certainty on the high temps; more on that below.

Breezy SE winds will also predominate, especially Friday and
Saturday as a pair of cyclones develop in quick succession in the
lee of the central Rockies, tightening the pressure gradient. May
even need to keep an eye out for potential Wind Advisory 
conditions along the I-69C/U. S. Highway 77 corridor Saturday 
afternoon. Stat guidance, usually a pretty good indicator for 
these conditions, for BRO/HRL hitting 24-25 knots. Haven't gone 
quite this high in the official grids yet, though. With winds 
remaining elevated Friday night, courtesy of 35-40KT H85 jet, we 
may even see record-high mins around 83-ish degrees Saturday 
morning. Just what everybody wants, right?

As far as rain chances go, not too much to talk about, but have 
inserted mentionable PoP's (though just slight chance) in a few 
periods. For Saturday night into Sunday, western portions of the 
CWA will reside on the NW flank of the upper high, which can be a 
favored area for convection. Moreover, a short-wave trough will 
be passing into south-central TX (per ECMWF), pulling a bit of 
moisture up with it. Looking ahead for Monday into Tuesday, the 
12Z run of the new GFS rebounds the upper-level ridge westward 
over the area, yielding a dry forecast, whereas the 00Z ECM 
developed a bit of a tropical tap of moisture in a weakness in 
the ridge. So, still some uncertainty in that timeframe; in fact, 
the 12Z ECM has backed off a bit on its PoP's. Even if just added 
cloud cover is realized, hopefully we'll back off of advisory- 
level heat.


.MARINE (Now through Wednesday Night): High pressure will prevail
across the Gulf of Mexico through Wednesday morning, with 
generally light to moderate southeast to south winds and moderate 
seas. The gradient will tighten Wednesday afternoon as low 
pressure deepens across West Texas. Small craft will need to 
exercise caution beginning from Wednesday afternoon through 
Wednesday night as winds ratchet up to 15 to 20 knots. Seas will 
build a foot or two Wednesday night in response to the stronger 

Thursday through Monday: Adverse marine conditions, especially for
the season, are expected through much of the period. A tight
pressure gradient will be in place between high pressure over the
eastern Gulf and thermal troughing over the continental interior.
The gradient will occasionally be enhanced by low-pressure centers
developing in the lee of the Rockies, as well. Right now, the
timeframe for strongest marine winds appears to be Friday night
into Saturday morning (poor timing for early morning fishing
trips), when wind gusts on the Gulf waters may exceed 25 knots. 
Small Craft Advisories are virtually certain for that time, as 
seas build to 6-8 ft. and remain elevated through Monday. 
Additional SCA's are likely to be needed periodically otherwise, 
beginning Thursday daytime on the Laguna Madre.


BAYVIEW/PORT ISABEL  80  94  81  93 /   0   0   0   0 
BROWNSVILLE          80  96  82  96 /   0   0   0   0 
HARLINGEN            79  98  81  99 /   0   0   0   0 
MCALLEN              79 102  81 102 /   0   0   0   0 
RIO GRANDE CITY      78 106  80 106 /   0   0   0   0 
SOUTH PADRE ISLAND   82  87  83  87 /   0   0   0   0 




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