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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 251124 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
624 AM CDT Sat May 25 2019

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

.AVIATION...Only initial conditions were changed for this TAF
cycle. VFR to MVFR continue to be forecast with moderate to 
breezy surface winds and no convection. 

.PREV DISCUSSION... /issued 404 AM CDT Sat May 25 2019/ 

SHORT TERM (Today through Sunday): No significant changes have 
occurred to the large-scale synoptic pattern, and therefore, the 
forecast for this time period will be very similar to the one issued 
for 24 hours ago. 500 mb high pressure centered over the panhandle 
of Florida will remain the dominant weather factor over Deep South 
Texas and the Rio Grande Valley for the weekend. With this 
protective dome in place, and an influx of drier air steadily moving 
into the BRO CWFA from the east to the point that precipitable water 
values will fall to near an inch, dry weather will prevail with no 
showers and thunderstorms anticipated. Meanwhile, at the surface, 
with high pressure over the Gulf of Mexico interacting with thermal 
low pressure situated inland over Mexico, breezy onshore winds will 
occur, making already above normal daytime high and overnight low 
temperatures feel even hotter. 

Meanwhile, at the local beaches, with the Memorial Day holiday in 
place and large swells approaching from the southeast, a High Risk 
of rip currents and corresponding Rip Current Statement will be in 
place until around sunset this evening. 

LONG TERM (Sunday Night through Friday): The heat beat goes on
right through the end of May, with the more interesting question
whether 2019 can become the warmest/hottest on record in most
areas by the time we reach next Friday (see Climate section below
for an update). 

The big picture in the overall pattern to end May has changed
little: Memorial Day will see the back edge of the northeast-
southwest elongated mid level ridge centered over the northern
Gulf Coast/Florida Panhandle continue across the Texas coast with
a nice pocket of very dry air settling in...then hanging on into
Tuesday. By Tuesday evening, the edge of an ejecting shear axis
from the persistent southwest U.S. trough slides across west Texas
then on into north and east Texas by Wednesday. This should help
fire up convection on the Sierra Madre each evening, and there is
an outside chance that some of this could graze Zapata and perhaps
Jim Hogg County. That said, the ability of any convection to slide
that far east will likely be held off by the back of the ridge
which never quite breaks will continue to not mention
rainfall during this period.

Thereafter, the ridge flattens across the southeastern U.S. and is
squeezed southward across the entire Gulf of Mexico by Thursday
and next Friday and farther back into northern Mexico, eventually
reaching toward Baja California. This should finally start to
relax the "Valley Wind Machine" for a couple of days anyway but
there's no notable change in the sensible weather as the
atmosphere maintains the dome of hot and rain-free conditions.
Deep tropical moisture may begin cranking up underneath the ridge
in broadening easterly flow, but this would favor the western
Caribbean through the Bay of Campeche on into Veracruz beyond this
forecast period.

For the sensible weather, then: More of the same through
Wednesday: Hot, breezy to locally windy days and sultry nights
with a continued fresh southeast breeze. With aforementioned drier
air pockets Monday through Tuesday, expect a bit more sunshine
including between IH 69C and IH 69E which has seen a mix of clouds
and some sunshine late this week. Temperatures should have no
trouble reaching the mid to upper 90s just about everywhere except
the beach each day, and remain in the upper 70s to lower 80s for
much of the night before dipping just below 80 (Rio Grande Valley
area) each morning.

For Thursday and Friday, winds should back a little to the east-
southeast and dip into more reasonable levels. But not seeing
enough of a signal to drop daytime temperatures any more than a
degree or two compared with Monday-Wednesday. Lows may dip a
degree or two given slightly lower winds.

The dry pockets will keep heat index values from surging too much,
with 100 to 105 the general rule by day. Evenings into overnights
are a slightly different story, with lower 80s temperatures and
mid to upper 70s dewpoints keeping "feels like" temperatures in
the upper 80s to lower 90s well into each night and toward the wee
hours. The A/C will still be humming.

Other issues of concern: For the beach, while tidal concerns have
eased with lower astronomical tides and persistent upshore flow
allowing departures from predicted to fall back to around 0.5
feet, the threat of dangerous south to north longshore currents, 
and perhaps a few embedded "reverse" rips near the Isla Blanca 
jetty, will close out the holiday weekend and likely continue into
at least Wednesday. Rip current statements may be extended or re-
issued as conditions warrant through Monday. 

For those inland, moderate air quality due to continued southeast
flow of residual soot/haze from agricultural burning in Mexico
will continue to be a nuisance issue through Wednesday. East-
southeast flow thereafter may finally bring a deeper blue sky for
the end of the week along with "good" air quality. 

MARINE: Now through Sunday: Buoy 42020 reported southeast winds 
around 19 knots gusting to around 25 knots with seas slightly over
6 feet with a period of 8 seconds at 250 CDT/750 UTC. An enhanced
pressure gradient will continue to produce strong winds and rough
seas along the Lower Texas Coast today, with Small Craft 
Advisories in effect. Tonight, and especially on Sunday, the 
gradient will ease slightly, resulting in lighter winds and lower 
seas. For this time period, Small Craft Exercise Caution is 
likely, however, Small Craft Advisories cannot be ruled out. 

Sunday Night through Wednesday Night...Gradient between modestly
strong surface ridge along the northern Gulf coast with daily
mountain troughs near between 995-1000 mb over north central
Mexico will keep gusty south/southeast winds going over the warmer
Gulf waters...slightly lower in the nearshore waters where winds
will be knocked down by a relatively robust marine layer based on
upwelling of cooler waters in the persistent south/southeast flow.
This means flirting with Small Craft Advisory winds each overnight
in the Gulf (18 to 22 knots) with plenty of wind waves and a
persistent 3 to 4 foot swell and 7-8 second swell period likely. 
Winds and seas will do a diurnal dip each afternoon but not enough
to improve conditions for comfortable trips out for small craft. 

Laguna Madre winds will also flirt with 20 knots each afternoon
before dipping back to 15 knots and gusty overnight until just
before daybreak. Caution wording will be most likely here for most
of the period. Wednesday night should see some improvement but
still moderate level winds/seas/chop as the gradient continues
even as winds back a tad to the east/southeast.

CLIMATE...As of this morning, Brownsville had pulled within 0.2
degrees of the 2003 record. Harlingen had moved into 4th place and
was closing on on 3rd while McAllen moved up to number 8 in a tie
for 7th. Looking back of the prior record from 2003, the big
difference this year from then was the end of the month, where
temperatures actually fell a bit below average after a hot first
half. This year features a hot start and a briefly cool spell with
the May 10-14 cloudy/locally stormy period. But the sultry nights
have brought daily averages to 5-6 above normal since the 19th,
and these levels will continue at 4-5 above through the 31st, all
but ensuring that many stations will be at or near new May records
when all is said and done.

TX...High Rip Current Risk through this evening for TXZ256-257-351.

GM...Small Craft Advisory for winds from 10 AM this morning to 7 PM 
     CDT this evening for GMZ130-132-135.

     Small Craft Advisory until 1 PM CDT this afternoon for GMZ150-


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