Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 301130 AAA
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
630 AM CDT TUE AUG 30 2016
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Just a few cosmetic adjustments to the previous set of
TAFs. VFR continues to be largely anticipated today with veering
winds courtesy of weak surface low pressure along the Lower Texas
Coast. The progression of this feature west into Deep South Texas
and the Rio Grande Valley will spark showers and thunderstorms for
the afternoon hours today. More tranquil conditions are expected
tonight as the loss of daytime heating ends the threat of convection
.PREV DISCUSSION... /issued 411 AM CDT TUE AUG 30 2016/
SHORT TERM (Today through Wednesday): A burst of convection is noted
over the Middle Texas Coast, wedged in between closed 500 mb low
pressure over the Upper Texas Coast and weak surface low pressure
along the Lower Texas Coast. Scattered showers and thunderstorms are
anticipated today across Deep South Texas, the Rio Grande Valley,
and the adjacent coastal waters as the surface low weakens and moves
west across the inland portion of the BRO CWFA while interacting
with daytime heating and deep tropical moisture in place. Tonight,
the precipitation becomes mainly a coastal affair, as the loss of
daytime heating kills most of the opportunity for precipitation
inland, but the southward progression of the 500 mb low maintains
scattered showers and thunderstorms for the adjacent coastal waters.
The proximity of this low, as well as another round of daytime
heating of deep tropical moisture, will maintain the threat of
scattered convection across the entire forecast area for Wednesday.
Daytime high and overnight low temperatures will be a bit tricky and
will depend on just how much cloud cover and precipitation occurs,
but generally near normal values are forecast for the period.
LONG TERM (Wednesday Night through Monday)...Little change to the
going forecast for the first half of the period which takes us
through most of the Holiday weekend. As the pesky upper level low
weakens and ultimately dissipates underneath the rebuilding 500 mb
ridge, showers and storms will fade away as well. Wednesday night
and Thursday remain a bit tricky as GFS continues to indicate a
fairly notable shear axis stretching back across the RGV from
what`s left of the center of the upper low about 100 miles
offshore, with enough moisture pooled along it to maintain
isolated to scattered activity, with the most coverage in
northeast Tamaulipas and perhaps still sneaking across the Rio
Grande. The ECMWF shoves the deeper moisture a bit farther south
as deepening northerly flow does the job. Still, given proximity
of moisture field elected to hold onto the mention of
precipitation along with a mix of clouds and sunshine. Temperature
forecast a bit dicey as the "drier" ECMWF punches triple digits up
away from the coast. A bit reluctant given the residual moisture
and time of year so held just below, a hair above the GFS.
The ridge builds in more solidly Thursday night and Friday as
upper trough reaches the eastern seaboard and quickly picks up
what is now Tropical Depression 9 and rips it along the Carolina
Coast by then. Drier air behind the departing TUTT and on the
front side of the Texas ridge should kill off most precipitation,
though with calm to light winds to start each day elected to hang
onto a slight chance for the mid Valley each day through Sunday.
With increasing sunshine, triple digit afternoon temperatures
should return to areas mainly along/west of US 281 each day.
Persistently lower GFS temperatures this summer were rejected in
favor of the warmer ECMWF, though values were fairly similar
toward the coast. In a sense, September will pick up where August
left off (see Climate section below).
By Sunday night and on into next Monday, the eastern ridge takes
control and elongates from north to south across the southeast
U.S. as a piece of the eastern U.S. trough hangs back over the
Carolinas, potentially capturing and enhancing what would be
Hermine east of the mid Atlantic. West of the elongated ridge,
southwest flow ahead of an early season Pacific Northwest trough
develops...and farther south in Texas, south to southeast flow
around the 500 mb ridge appears to slowly set up. Both GFS/ECMWF
show a brief period of deepening moisture on the backside,
favoring the Coastal Bend through Southeast Texas but with
increasing mean relative humidity to the eastern third of Deep
South Texas. With this in mind, increased coverage of rain chance
area, added more clouds, and lowered temperatures back to `normal`
(mid to upper 90s all areas) for Labor Day.
MARINE: Buoy 42020 reported South winds around 12 knots gusting
to around 14 knots with seas slightly over 3.5 feet with a period
of 6 seconds at 03 CDT/08 UTC. Moderate swells from the east-
northeast, produced by a long fetch of breezy winds from the same
direction across the entire Gulf of Mexico, will affect the Lower
Texas Gulf of Mexico waters throughout the entire forecast period.
Light to moderate winds are also forecast with weak surface low
pressure dissipating over the western Gulf of Mexico and leaving a
weak pressure gradient in its wake. Small Craft Exercise Caution
and Small Craft Advisory are not expected to be needed.
Wednesday Night through Saturday: About the only concern will be
through Thursday, with combination of residual swell from
scattered to numerous showers/storms across the waters prior to
the start of the period as well as the general surface low
associated with the TUTT feature which keeps a modest but notable
northeast/east flow going. The precipitation should fade away
later Thursday and continue fairly rain free through the weekend,
with seas becoming slight in time for boaters and fishers to
enjoy the first half of the Holiday Weekend.
CLIMATE...Even with the final two days of the month likely to
settle near or just below the 30 year average, most Valley sites
will rank among the top five all-time warmest for August.
Brownsville ranked #3 (86.9 overall average) and McAllen #2 (90.9
overall average) through the 29th. More interesting were when the
a number of the top values occurred. For Brownsville, the hottest
August was in 2011, followed by 2010, 2016, and 2014 (through the
29th). For McAllen/Miller, the hottest was 2009, followed by 2016,
2015, 2011, and 2012.
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