Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 211450 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
950 AM CDT SUN AUG 21 2016

.DISCUSSION...Updated the forecast for the latest trends,
especially out west. Up front...cancelled the Flash Flood Watch
for Brooks County but maintained it for Jim Hogg and Zapata until
7pm. The heaviest rain has shifted northwest but additional
convection is developing over Eastern Zapata and much of Jim Hogg.
3 to 7 inches fell overnight and an additional 1 to 3 with
isolated higher amounts possible. Adjusted pops out west to
coincide with the Watch and kept the low chances out east and in
the RGV. showers are beginning to develop along and east of Padre
Island as moisture transport is higher then expected probably due
a deeper southerly flow east of mid level low pressure area over
Nuevo Leon. Will continue to monitor as we might have to update
later this morning for higher rain chances across the RGV.
Finally, lowered temperatures out west with the rain and thicker
cloud cover. Did not adjust in the RGV thinking that the thicker
cirrus will have a tendency to thin through the day allow for
sufficient heating plus the region is staring warmer with lows
only in the low to mid 80s.

&&

.PREV DISCUSSION... /issued 709 AM CDT SUN AUG 21 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Mid and High level cld cover associated with the
convection firing to our northwest will move southwards over the
RGV through the day. The convection to our north has not shown
much progress pushing southwards as the 500 mb ridging is
maintaining a little more stable atms over the RGV. Daytime
heating later today after sunrise may destabilize the atms enough
to allow some isolated convection to form up across the RGV.
Expect any convection that forms to likely miss the RGV airports
during the afternoon. So will not include any vcts or tempo groups
for convection later in the current TAF period.

PREV DISCUSSION... /issued 433 AM CDT SUN AUG 21 2016/

SHORT TERM (Now through Monday): 500 mb ridging will remain in
place over the Gulf of Mex and the Gulf coast region with more
weakness in the ridge axis evident further inland over Texas and
north central Mexico where the deeper moisture values reside. The
500 mb ridge axis over the Gulf of Mexico will start to build
westwards later tonight into Sunday which will then shift the
better moisture values further west allowing for drier weather to
prevail into Monday.

For the immediate short term...slow moving convection continues to
fire in the deeper layer moisture values located just to the north
and west of Deep South TX. The convection is being helped along by
an old surface boundary that is located over portions of southern TX
stretching roughly from the western counties of Deep South TX
extending northeast.  KBRO radar trends indicate the this convection
is nearly stationary or is backbuilding a bit more to the southwest
into northeast Mexico. This will likely enhance the potential for
additional heavy rainfall/flash flooding problems for portions of
the northern and western counties. So will post an FFA for
Zapata...Jim Hogg and Brooks counties for today.

Further to the south and east of the ongoing convection the 00z BRO
sounding shows much drier air in place closer to the coastline which
is closer to the 500 mb ridge axis. So will go with much lower pops
across the rest of the BRO cwa as numerical guidance from the
GFS/NAM and ECMWF all point towards much lower pops for these areas
for the rest of the weekend.

For temps the short term guidance is in pretty good agreement
throughout today and tomorrow for both highs and lows. So will go
with a general model blend for temps through Monday.

LONG TERM (Monday Night through Saturday): No significant changes
to the long term forecast. Upper level high pressure is expected
to continue to track westward over the Gulf and dominate the
region with drier air and a general subsident pattern. Flow will
be SSE around the high pressure system and should shutoff any
seabreeze effect through much of the week. By late in the
period...the high will shift more north and west...allowing more
have an easterly component and for weak impulses and a bit more
moisture to return. As such...have kept at least some slight
chance POPs for Friday and Saturday. Temperatures are expected to
range near or above normal...with some triple digit values
continuing for McAllen and the upper portions of the RGV and
Ranchlands.

MARINE:

Now through Monday: The surface high pressure area centered over
the Gulf of Mexico and the eastern U.S. will maintain a moderate
PGF across the lower Texas coastline throughout today and Monday.
This will result in some SCEC conditions for the bay and gulf
waters throughout the short term. Conditions may flirt with SCA
criteria briefly for either the bay or gulf areas but will not
post up an SCA at this time.

Monday Night through Thursday Night: Upper level high pressure
will build westward across the northern Gulf waters through the
period. Light to moderate winds will become more SE to SSE as the
high pressure creates more of a southerly flow. Seas will remain
more moderate through early Wednesday given the possibility of a
longer SSE fetch. As the high pressure broadens over the
region...the pressure gradient will lessen and the winds and seas
will begin to relax late Wendesday into Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  94  80  93  81 /  20  10  10  10
BROWNSVILLE          95  79  95  80 /  20  10  10  10
HARLINGEN            98  78  97  79 /  20  10  10  10
MCALLEN             100  78  99  80 /  20  10  10  10
RIO GRANDE CITY      94  77  99  79 /  30  30  10  10
SOUTH PADRE ISLAND   90  82  89  82 /  20  10  10  10

&&

.BRO Watches/Warnings/Advisories...
TX...Flash Flood Watch until 7 PM CDT this evening for TXZ248-249.

GM...None.
&&

$$

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