Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 300555 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1255 AM CDT Sun Apr 30 2017

.DISCUSSION...Cold front quickly making its way across the CWA
from NW to SE, roughly on a line from MFE up into central Kenedy
County at this time. Issued a Wind Advisory about an hour ago,
valid until 2am for Zapata, Jim Hogg, Brooks, and Starr counties
and from 1am until 5am for the remainder of the area. Winds and
gusts only meeting advisory criteria for an hour or two along and
behind the front, but will let the advisory ride for now.

Also extended the High Surf Advisory through 1pm, though difficult
to get much "ground truth" at this hour. NWPS Gerling-Hanson plots
and WW3 spectral bulletins for Buoy 42020 indicate that the
significant SE swell (with dominant period of 9-10 seconds) will
continue through around mid-day Sunday, even as winds become N
behind the cold front.

&&

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

&&

.AVIATION...Main challenge with this cycle is timing FROPA into
the aerodromes, though even that is fairly straightforward at this
point. Gusts up to 35-40 knots have been occurring upstream with
the front, though some of these have been convectively aided and
even then only occurring for an hour or two. Expecting gusts right
around 30KT at the airports (shy of AWW criterion), commencing
shortly at MFE, then into HRL and BRO between 07-08Z. Current MVFR
CIG`s should lift to VFR by 10-12Z with more moderate N winds
lasting through much of the daytime before veering light NE in the
evening.

&&

.PREV DISCUSSION... /issued 634 PM CDT Sat Apr 29 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...High cirrus is passing over Deep South Texas and the
Rio Grande Valley right now, while breezy winds prevail at the
surface. The passage of a cold front overnight tonight will bring
veering winds and brief MVFR cloud decks. Full VFR will be in
effect on Sunday with high pressure building in from the north,
allowing for winds to diminish to more moderate levels.

PREV DISCUSSION... /issued 243 PM CDT Sat Apr 29 2017/

SHORT TERM (Tonight through Sunday Night): Strong, dusty, gusty winds
will subside by this evening as high pressure behind an approaching
cold front fills in the daytime low pressure depression over West
Texas. Mdt south southeast winds will continue overnight, however,
pretty much until they shift to northwest with the arrival of the
cold front. The front should reach the Upper Valley around midnight,
pushing to Brownsville and offshore before dawn. The best chance for
any precip will be a brief window along the front, and even those
chances may not be very significant except for possible isolated to
scattered shower activity on the Island and near Brownsville around
dawn.

Winds will swing around to strong northwest behind the front, but
only very briefly. Winds will diminish quickly over a period of a
few hours to mid morning. Skies will become sunny but temperatures
should remain in a more normalish mid 80s range. Sunday night will
be clear with low temperatures dipping below normal to around 60
degrees.

LONG TERM (Monday through Saturday): 500mb low/trough moving
eastward across the midwest United States Monday will provide
subsidence across Texas early next week. Low to mid level moisture
will increase across south TX Tuesday into Wednesday as a 500mb
trough develops across northwest Mexico Tuesday and another upper
level trough develops across the Rockies Wednesday. This will
provide a good chance of showers and thunderstorms...some possibly
strong to severe...late Wednesday into early Thursday as the upper
level trough across the Rockies moves eastward across south-
central U.S. Thursday bringing a cold front through deep south TX
early Thurs morning. Will go ahead and increase rain chances late Wed
night as a result. Drier and slightly cooler air will filter into
the CWA in the wake of the front Thursday. This will provide
relief to the above normal temperatures Monday through Wednesday
with near normal temps Thursday and Friday. Above normal temps
return towards the end of the forecast period.

MARINE (Now through Sunday night): Strong south southeast winds
will subside to moderate late tonight before shifting to northwest
or north after midnight when a cold front plows through the region.
Advisory conditions will necessarily continue on the Gulf due to
elevated wave heights, but winds may dip below 20 knots for a few
hours on the Laguna Madre. High pressure will spread over the Gulf
quickly on Sunday, with improving conditions through the day. Seas
will abate more slowly, and advisory conditions on the Gulf may be
forestalled until Sunday evening or Sunday night.

Monday through Thursday...Light east to southeast winds will
prevail across the coastal waters Monday as surface high pressure
across the northwest Gulf coast moves eastward. The pressure
gradient will increase across the lower Texas coast Mon night as
low pressure develops across west TX and high pressure moves
across the northeast Gulf coast. Moderate to strong southeast
winds will prevail across the western Gulf of Mexico Mon night
before the pressure gradient weakens slightly Tuesday. Moderate
southeast winds should prevail across the lower TX coast Tuesday
and Wednesday before a cold front moves offshore late Wed night
into early Thurs morning. Strong north winds will develop in the
wake of the front Thursday. Small craft advisories may be needed
for the offshore waters Mon night and will likely be needed for
all of the coastal waters Thursday.

FIRE WEATHER...RH values will crash to 15-20% west of US 77/I-69E
Sunday in the wake of an assertive dry air mass arriving late Sat
night/Sunday morning. Winds at 20 feet are forecast to be in the 10
to 15 mph range Sunday during the nadir of RH values, slightly less
than required for critical levels. Wildfire growth and spread may be
marginally enhanced on Sunday, but will hold off on any products for
now.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory until 2 AM CDT early this morning for TXZ248>250-
     252.

     High Surf Advisory until 1 PM CDT this afternoon for TXZ251-256-
     257.

     Wind Advisory until 5 AM CDT early this morning for TXZ251-
     253>257.

GM...Small Craft Advisory for winds from 4 AM early this morning to
     noon CDT today for GMZ130-132-135.

     Small Craft Advisory until 1 PM CDT this afternoon for GMZ150-
     155-170-175.

&&

$$

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