Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 232031
Area Forecast Discussion
National Weather Service BROWNSVILLE TX
331 PM CDT SAT JUL 23 2016
.SHORT TERM (Tonight through Sunday Night): Short-term forecast
continues to be more-or-less steady-state. Broad 500-mb high
currently centered over NM continues to exert its influence on the
area. Just a handful of light showers have developed early this
afternoon along and just behind the sea-breeze front. SE surface
flow has kept areal coverage of said showers down a bit (from
already low levels) from last couple of days. Short-term models
have captured this well.
Not much change for tomorrow, with center of mid-level high and
local thickness values basically unchanged. Hot conditions will
continue with afternoon heat indices reaching 105-110 degrees across
much of the area. GFS keeping precipitable water values in the 1.7-
1.9" range, whereas NAM brings in a modest batch mid-level moisture
for slightly higher values. MET PoP`s in the 15-20% range while MAV
are single-digits. In the grids, have limited mentionable PoP`s to
the offshore waters late night/early morning both nights and inland
areas (though not at the coast) Sunday afternoon.
.LONG TERM (Monday through Saturday): In the grand scheme of
things, more of the same as late July swelter continues virtually
uninterrupted. The devil is in the details, particularly on
Tuesday and Wednesday. Slight discrepancies arise between the GFS
and ECMWF with handling of weak inverted 500 mb trough that slides
across the northern Gulf Tuesday into Wednesday. The GFS has been
consitently and even trending more bearish on rain chances for the
southern tip of Texas, keeping the deepest moisture within the
core short waves from southeast and east Texas through southern
Louisiana. The ECMWF comes up with a third short wave "center"
over south Texas on Tuesday which moves steadily westward and on
into south and central Texas and the Big Bend by Wednesday, with
likely some orographic forcing kicking up the mean RH and precip
well west and north of the RGV by then.
Climatologically, recent trends, and reasons for the additional
southern wave indeterminate lead us to lean on the low side of
rain chances, mainly held to Tuesday but giving a very slight nod
to Wednesday afternoon farther west if any residual moisture
remains. If the GFS is correct, the only rain would fall in
overnight/early morning streamer showers from southeast to
northwest, reaching the coast before dissipating in too strong of
a southerly flow similar to what brought us the first 2+ weeks of
rain- free weather to start July.
For the sensible weather, Monday should be rain-free except for
the usual warm waters of the Gulf and temperatures continuing the
"new" streak of triple digit afternoons along and west of U.S.
281/IH 69C. For Tuesday, reluctantly held slight chances for areas
east of U.S. 281/IH 69C through mid afternoon, though quite
possible the beaches clear out by noon as typical in a sea breeze
"jump" event. This assumes the GFS is not dead on; such a solution
would keep rain chances to a silent 10 percent (or less) away from
the coast as mentioned above. Based on the potential for a bit
of afternoon rain coverage as well as higher clouds which both
GFS and ECMWF show decent cirrus, have kept the triple digit line
across the Rio Grande Plains.
By Wednesday, with drier air filtering into the 1000-500 mb layer
and some thinning of the cirrus above, nudged highs back over 100
for U.S. 281.
Thereafter, the weak inverted trough exits stage left into western
Mexico, allowing the Canicular ridge to spill back over into Texas
beginning Thursday and continuing through the weekend as upper
level low dips into the northeast U.S., which helps said ridge`s
cause in maintaining the rain-free, hot, and somewhat breezy days.
Breezes may slacken a bit by Saturday. Temperatures edge a little
higher, close to the 96 Brownsville/99 Harlingen/102 McAllen
common theme through the second week of July.
One note: Should Tuesday (and/or Wednesday) remain at or above 100
in McAllen, theres no evidence thereafter for afternoon
temperatures to dip below that through the next two weeks. A
second streak could be well underway by month`s end. Stay tuned...
.MARINE: Tonight through Sunday Night: Relatively slack pressure
gradient between broad high pressure across the Gulf of Mexico and
modest thermal troughing in the Desert Southwest will yield winds
mainly on the moderate side. Tropical waves crossing the Yucatan
and Bay of Campeche will "dent" the Gulf high a bit for wind
directions from the SSE. Winds on the Laguna Madre could approach
SCEC criterion on Sunday afternoon, but otherwise no marine
headlines are expected. Seas run in the 2-3 ft. range. Isolated
showers still a possibility between midnight and mid-morning each
Monday through Thursday: The main issue will be how much and when
the south/southeast flow builds through the period. As mentioned
above, ECMWF`s handling of a third wave moving through Deep South
Texas/Lower Texas Gulf waters would keep flow down a bit Tuesday
and Tuesday night, while the GFS kicks up winds with tightening
surface gradient. Decided to split the difference with some
afternoon pickup over Laguna Madre, and marine layer knocking that
down over the nearshore waters; in all cases, near but just under
caution (15-20 knot) levels.
For Wednesday and Thursday, broader southeast flow will ease surf
and nearshore water temperatures back down a couple of degrees or
more, which will help keep daytime winds in check in the zero to
20 nm waters. Laguna winds may edge into caution levels each
afternoon. With no broad swell expected, some nearshore
windswell/wind chop and general uptick of winds will build seas a
bit, but should remain below 5 feet through the period. Periodic
showers mainly offshore will continue as they have, but move from
south to north rather than east to west.
.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL 80 93 80 92 / 10 10 10 10
BROWNSVILLE 79 95 79 96 / 10 10 10 10
HARLINGEN 77 98 77 99 / 10 10 10 10
MCALLEN 79 100 79 101 / 0 10 0 10
RIO GRANDE CITY 78 102 78 103 / 0 10 10 10
SOUTH PADRE ISLAND 81 90 81 87 / 10 10 10 10
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