Excessive Heat and Heat in Texas, August 16 to 20, 2023

Area Forecast Discussion
National Weather Service Corpus Christi TX
1209 PM CDT Wed Aug 16 2023

...New AVIATION...

.SHORT TERM...
(Today through Thursday)
Issued at 342 AM CDT Wed Aug 16 2023

GOES imagery of total precipitable water shows an axis of higher
moisture from the northwest Gulf of Mexico westward across south
Texas with PW values near 2 inches over the Gulf to 1.8 inches
over the Brush Country. But imagery also shows much drier air over
central and east Texas. This drier air is expected to filter into
the northern Brush Country to the Victoria Crossroads this
afternoon. Models show a very weak mid level vorticity axis moving
into the region this afternoon. With moisture and instability
available across the southern tier of counties, expect isolated
convection will develop this afternoon that will drift to the
southwest. Will keep a slight chance of storms into the early
evening hours for the southern Brush Country.

It will be hot again with record highs expected at CRP today. But with
the drier air moving into the Victoria Crossroads, do not expect
afternoon heat index values to reach advisory levels. Expanded the
Heat Advisory for the northern portion of the Coastal Bend to the
northern Brush Country from 1 to 7 PM.

With drier air in place tonight along with light winds, lows will
fall into the lower to mid 70s over the inland coastal plains
early Thursday morning. Models show PW values well below normal
on Thursday with some areas below 1 inch by the afternoon. With
deep mixing, afternoon heat index values may struggle to reach
advisory criteria. Forecast shows HI values around 110 Thursday
afternoon mainly for the inland coastal plains. With drier air
in place, expect highs will be a degree warmer inland Thursday.

Afternoon RH levels will fall 15-20 percent over the Brush Country
and 25-35 percent for the inland coastal plains. As winds increase
with the sea breeze during the afternoon, elevated fire danger
conditions could develop over the inland coastal plains and linger
into the mid evening hours for the Brush Country.

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 342 AM CDT Wed Aug 16 2023

Key Messages:

 - Dangerous heat going into the weekend
 - Elevated to Critical Fire danger possibly Friday
 - Rain chances increase into early next week
 - Tropical system Monday/Tuesday

As mentioned yesterday, changes are afoot. With each successive run
of the models, the chances for rain and tropical waves getting into
South Texas increase, and the chances for temperatures to trend down
for a bit. Hear are the details...

The 500 mb ridge, Thursday night, is still in place as it has been,
although, now that the 500 mb trough to the east is beginning to
lift the ridge is expected to slowly move to the east. So the ridge
is moving from southern CO/northern NM, to the mid-Mississippi
Valley by Monday morning. This opens up the easterly 500 mb winds
over the entire Gulf, rather than the southern part, and allow the
tropical waves to move into the Gulf from the Caribbean. Friday,
as the ridge begins to move, the min RH continues to be <25% in
the Rio Grande Plains and the western Brush Country. The Coastal
Plains will be around 35-40% for the minimum RH, problem then
becomes the coordination between the winds and the RH. With the
winds picking up late in the afternoon/early evening, it doesn't
look like we would get to critical thresholds at the same time.
The low RH will be during the afternoon, while the winds will be
in the evening. So probably looking at an elevated situation.

Once we get into the weekend, the chance for precipitation begins to
go up gradually. First the the increase is in the marine areas off
shore, and creeping towards the land. Models keep the rain out of
here Saturday and Sunday, so we should be good. Monday the rain
looks like it will creep into the islands along the Coastal Bend,
before getting onshore during Monday evening into Tuesday. Much
of the tropical wave that is expected to develop is unknown.
Looking at the models the CMC and GFS have similar tracks, but the
GFS makes landfall around BRO, while the CMC is farther south.
The ECMWF now has the wave in the northern part of the Gulf. NHC
has the wave at a 20% chance of development over the next 7 days,
so it will be watched.

With the rain the temperatures will come down a for a bit with highs
expected into the 90s(Lower 90s?) this looks to keep the area out of
heat warnings for the time being, but advisories are still likely.

&&

.AVIATION...
(18Z TAFS)
Issued at 1154 AM CDT Wed Aug 16 2023

VFR conditions are currently in place across all terminals. Drier
air will continue to work into the region so expect VFR through
the period. The only exception would be the development of some
isolated showers and storms this afternoon, generally across the
Coastal Plains, where the deepest moisture resides. Winds will
gradually turn out of the south overnight while remaining less
than 10 knots.

&&

.MARINE...
Issued at 342 AM CDT Wed Aug 16 2023

Weak offshore flow this morning will become weak to moderate
onshore this afternoon with the development of the sea breeze.
The onshore flow will become weak for the overnight hours tonight
into Thursday morning. A weak to moderate onshore flow will occur
again Thursday afternoon.

Through the weekend, the wind looks to follow the diurnal
cycle that has been prevalent through most of this season so far.
That cycle is generally a weak to moderate south flow that turns SE
by the afternoon and increases to moderate or moderate to strong
flow during the late afternoon/early evening. Winds then diminish
overnight to weak to moderate flow and the winds veer back to the
south again. There is an uptick, after the weekend, of the pops with
chances of showers and thunderstorms either in the offshore zones,
or all the way up to the shore. It does look like there could be a
tropical wave that moves into western Gulf bringing rain to the
Coastal Bend, Monday night/Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi   101  77 100  78 /  20   0   0   0
Victoria         104  75 104  75 /  10   0   0   0
Laredo           107  80 108  79 /  20  20   0   0
Alice            106  74 107  74 /  20  10   0   0
Rockport          96  80  95  80 /  10   0  10   0
Cotulla          107  79 108  77 /  10  10   0   0
Kingsville       104  75 104  76 /  20  10   0   0
Navy Corpus       96  81  96  81 /  10   0   0   0

&&

.CRP WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 7 PM CDT this evening for TXZ229>232-239>246-
     342>344-346.

GM...None.
&&

SHORT TERM...TMT
LONG TERM....JSL
AVIATION...TC/95