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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 240928

Area Forecast Discussion
National Weather Service Brownsville TX
428 AM CDT Fri May 24 2019

...The heat and wind go on and on and on as May set to end in the
top ten warmest on record...

.SHORT TERM (Today through Saturday): No change expected to the 
current blast furnace conditions. Deep South Texas and the Rio 
Grande Valley will continue to be dominated by 500 mb high pressure 
centered roughly over the Florida Panhandle, resulting in continued 
dry and hot weather. Meanwhile, at the surface, high pressure over 
the Gulf of Mexico will interact with thermal low pressure over 
inland Mexico. The resulting breezy to windy onshore flow will cause 
already above normal ambient temperatures to feel even hotter. 

At the local beaches along the Lower Texas Coast, a Rip Current 
Statement will be in effect through at least sunrise Saturday 
morning for a High Risk of rip currents. This will be due to swells 
impacting the beaches of South Padre Island and Boca Chica Beach at 
a time when there is an increased number of beachgoers for the 
Memorial Day holiday weekend. 

.LONG TERM (Saturday Night through Thursday): The forecast has
changed little over the past 24 hours and beyond...with the only
exception to remove mentionable precipitation for the middle to
end of next week. North to south elongated (and parked) southeast
U.S. and northern Gulf 500 mb ridge through Saturday becomes more
east-west oriented Sunday, with center shifting a bit farther east
Monday as back edge continues to extend to the Texas coast. Shots
of deep dry air press west across the Rio Grande Valley each
afternoon, while short waves riding between the ridge and southern
Rockies trough both reinforce the surface pressure gradient and
increase atmospheric heat Monday into Tuesday as thickness and
low level temperatures continue to rise.  

The 500 mb ridge continues to flatten along coastal Texas into
early Wednesday but never cedes control especially across the Rio
Grande Valley and Deep South Texas. Any Sierra Madre convection
Tuesday and Wednesday should ride north/northeast and refocus much
farther north along the northern periphery of the ridge into
Thursday, which by then has rebuilt fully on an east-west axis
through all of south Texas. For this reason, have removed
mentionable rain chances as the combination of deep dry air and
too much wind in the low levels is hostile for any precipitation.

For the sensible weather...the Valley Wind Machine persists
through Wednesday, with 15 to 25 mph and gusty on land for all but
the wee hours each day. The heated up atmosphere combined with
high sun angle and drying soils should allow high temperatures to
reach the upper 90s across much of the populate RGV Sunday through
Wednesday, and it wouldn't surprise if McAllen/Miller airport
poked 100 one or more of those afternoons. Expect more afternoon
sunshine and evening clear skies, with the possibility of low
clouds streaking through in the continued breezes overnight
through Wednesday morning. The clouds if they occur could keep
temperatures from falling below 80 in many areas of the Valley but
for now have held minimum temperatures just below that. Despite
the actual temperatures, the mix-down of the aforementioned drier
air should keep heat index in check...still well above late May
averages but below 111 advisory criteria. In general, 100 to 105
each day through Tuesday, then potentially increasing a bit
Wednesday as a touch more low level moisture reappears then. 

As for Thursday...elongated east-west ridge stretches from the
northern Bahamas through Baja California, which should also
reorient the positio of the eastern Gulf surface high and extend
it farther west. This should finally reduce surface winds a bit
and back them toward the east-southeast...a more typical summer
pattern as June is on the doorstep. Temperatures look to be a
shade lower as well but still several degrees above average both
day and night.

Air quality should improve incrementally through Tuesday with the
mix-down of drier air, but some haze and still moderate fine
particulates are likely as low level flow remains south/southeast.
More azure tropical blue skies *may* arrive Thursday if east
southeast flow can arrive.

Finally: Threat for intense longshore currents will continue at
the beach right through Memorial Day, with "reverse rip" on the
north side of Isla Blanca jetty. A reverse rip is water that
moves around the jetty and then returns toward the beach from the
northeast, which has been a significant danger in the past. Rip
current statments will likely continue for the balance of the 
weekend given expected crowds.


.MARINE: (Today through Saturday)...Buoy 42020 reported southeast
winds around 21 knots gusting to around 27 knots with seas 
slightly over 8 feet with a period of 8 seconds at 250 CDT/750 
UTC. Adverse marine conditions will prevail along the Lower Texas 
Coast for the period due to the interaction of high pressure over 
the Gulf of Mexico and low pressure over inland Mexico. A Small 
Craft Advisory for Winds will be needed for the Laguna Madre 
Friday and Saturday, with Small Craft Advisory also needed for the
Gulf of Mexico waters out to 60 nautical miles for most, if not 
all, of the aforementioned time period.

Saturday Night through Tuesday Night: Small craft exercise caution
for both wind and seas are likely early in the period as winds and
seas relax just a hair over recent days. That changes as gradient
sharpens on Memorial Day and especially Monday night through
Tuesday night. Gulf winds likely to run 20 knots or higher
overnight each day Monday and Tuesday, with seas recovering to 7
feet in may areas. Nearshore upwelling will continue to knock down
winds a hair but gradient and low level jet potential will keep
some breeze in play even there. Advisories are likely to be posted
Monday afternoon (Laguna Madre) and Monday night through Tuesday
night over the Gulf and perhaps Laguna (night) as well. Bottom
line? Just not the weekend...or early next week...for small craft
boating/fishing as wind waves, swell, and wind will all make
conditions difficult.


.CLIMATE...Most sites in the RGV are climbing through the top ten
warmest Mays on record and with the forecast through the end of
May of more of the same, Brownsville (since 1878) looks like a
lock for a new record as the difference between #1 (2003) and #2
(2019) had shrunk to just 0.5 degrees. For the year so far, 
Brownsville ranks #18 warmest, despite a cool March and just above
average January and April. May is catching the year up fairly

BAYVIEW/PORT ISABEL  92  81  93  79 /   0   0   0  10 
BROWNSVILLE          93  80  94  79 /   0   0   0  10 
HARLINGEN            97  80  97  77 /   0   0   0  10 
MCALLEN              97  80  98  79 /   0   0   0  10 
RIO GRANDE CITY      98  80  99  78 /   0   0   0  10 
SOUTH PADRE ISLAND   89  81  87  79 /   0   0   0  10 


TX...High Rip Current Risk through Saturday morning for TXZ256-257-

GM...Small Craft Advisory for winds until 7 PM CDT this evening for 

     Small Craft Advisory until 7 AM CDT Saturday for GMZ150-155-170-



This product is also available on the web at:

Short Term...66/JGT
Long Term...52/BSG
Graphics/Upper Air...Mejia