Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 220000 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
700 PM CDT SAT MAY 21 2016

.DISCUSSION...Made a few minor tweaks to re-orient rain chances
and adjust things like sky/wind for the coast this afternoon (now
over) and on Sunday, as pattern in the short term is settling into
a classic late spring/early summer sea breeze regime. This regime
keeps rain off the beach and begins any activity just west, from
Port Isabel to Bayview before quickly scooting northwest on the
low level southeast flow. With Gulf temperatures warming but still
some 15 degrees lower than the nearby land (79 vs. 94), and
synoptic overcoming unavailable with upper ridge rather than
trough building, expect lower speeds over the Gulf and beach while
winds are some 10 mph or so over land. Retained the 20 percent
chances for Sunday afternoon for now, though atmosphere looks
drier on the whole than today and coverage was ~20 percent at best
this afternoon.

Another thing to watch modestly is the heat index on Sunday
mainly for the Lower/Mid Valley. Poked 107-109 in many locations
today and may see another 105-108 type afternoon Sunday. Below our
advisory criteria (111) but notable, which will bring crowds to
the beaches once again. Light winds/modest surf keep danger low
for those cooling down in the Gulf. 52/BSG

&&

.AVIATION...Another somewhat tricky forecast for ceilings and even
visibility overnight and early Sunday. At least we won`t have to
deal with convection development in differential heating, since
that was wiped out with plenty of sunshine across the entire
region this afternoon. Last night`s GFS-20 was a bit touch-and-go
on RH at the based of the inversion, but tonight`s 18Z update has
near 100 percent sitting right along the IFR/MVFR line (1K feet)
at all three terminals; with this in mind have gone a bit more
pessimistic than previous forecast and brought in the low decks as
ceilings instead of scattered. Likely to see periods of haze/mist
but no more than high MVFR with no rain today; haze partly a
remnant of late season agricultural burning in southern
Mexico/Central America and will be an issue for the next several
days.

For Sunday, morning murkiness should lift to mainly scattered VFR
levels, lowest near the coast. No rain mentioned at this point as
region under subsidence and plenty of dry air above the cumulus
field. That field may well vary from scattered to broken but
didn`t want to add more to a somewhat lengthy TAF. Southeast winds
will pick up a bit on today, but gradient not super-established
and 850-925 winds near 20 knots, so gusts were the extent of the
wind differenct from today.
52/bsg

&&

.PREV DISCUSSION... /issued 207 PM CDT SAT MAY 21 2016/

SHORT TERM (Tonight through Sunday Night): The upper ridge
continues to build aloft across the area into the short term
period with a few perturbations within the upper flow. The
combination of this perturbation with abundance of moisture has
provided a favorable environment for isolated to scattered showers
and thunderstorms this afternoon along the coastal counties and
the RGV. These showers will continue to move northward at around
15 to 20 mph producing brief period of moderate rain shower and an
occasional lightning. Expect the activity to continue through out
the day providing a mix of sun and clouds keeping temperatures in
the mid to upper 90s with high humidity. A light Southeast flow
will prevail through the night with abundant cloud cover expected.
Expect another humid and warm night with temperatures in the mid
to upper 70s. On Sunday, as the ridge moves further E the gradient
will strengthen increasing SE winds in the afternoon. Lingering
moisture over the area and East of the Sierra Madre will favor for
convection Sunday afternoon mainly over the Western counties. Lean
toward 20 percent mainly along the W where the storms will begin
to develop. Rainfall accumulations will be less than a quarter of
an inch to half an inch. High temperatures will be in the mid to
upper 80s and near the 90s. Low temperatures will be ranging
between the mid to upper 70s.

LONG TERM (Monday through Saturday): The first half of the
period will be dominated by a weak upper ridge over deep south
Texas with its axis aligned north-south in the vicinity of the
coast. Aside from being precipitation free, rising
heights/thicknesses in the Mon-Wed timeframe will bring above
normal temperatures with seasonal dew points. The end result will
be mostly sunny/partly cloudy skies with hot/humid days and weak
surface winds.

On Thursday, the ridge will get nudged eastward as an upper trough
transitions eastward into the southern plains from the southern
Rockies. Increasing southwest flow aloft will cause moisture to
increase across deep south Texas while strengthening onshore flow
contributes additional moisture. Because of the moisture increase,
slight chances of precipitation enter the forecast again on
Thursday and remain in through Friday. Increasing moisture will
counter gradually lowering heights/thicknesses Thu-Fri for
continued above normal temps and humid conditions across the
board. A weak upper trough looks to move across deep south Texas
Friday afternoon/night followed by weak upper ridging for
Saturday. Have removed precip chances for Saturday based on the
trough passage with temps expected to remain somewhat above
normal.

MARINE: Now through Sunday night...Weak gradient will be weak
today keeping a Southeasterly flow across the Gulf Waters. A few
isolated showers will develop near the coast but produce mainly a
brief rain shower. Into Sunday the gradient strengthens increasing
southeast winds along the coast. Seas will build into the 3 to 4
feet range with possible SCEC over the Gulf waters and the Laguna
Madre.

Monday through Wednesday night: Modest winds/seas will prevail
along the lower Texas coast through the period with high pressure
over the western Gulf of Mexico. Small Craft Advisory and/or
Small Craft Should Exercise Caution conditions will develop
toward the end of the period as the pressure gradient strengthens.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  78  85  78  89 /  10  20  10   0
BROWNSVILLE          77  90  78  90 /  10  20  10   0
HARLINGEN            76  91  77  93 /  10  20  10   0
MCALLEN              77  93  78  95 /  10  10  10   0
RIO GRANDE CITY      76  95  77  97 /  10  10  10   0
SOUTH PADRE ISLAND   78  81  79  85 /  10  10  10   0

&&

.BRO Watches/Warnings/Advisories...
TX...None.
GM...None.
&&

$$

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