Area Forecast Discussion
Issued by NWS Lake Charles, LA

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FXUS64 KLCH 232251
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
551 PM CDT Wed Aug 23 2017

.AVIATION...Showers and storms will continue around the area
through the next couple of hours. This may produce periodic MVFR
conditions. After the convection dies off VFR conditions are
expected through Thursday Morning.


&&

.PREV DISCUSSION... /issued 438 PM CDT Wed Aug 23 2017/

..POTENTIAL FOR HEAVY RAINFALL AND FLOOD EVENT OVER THE
WEEKEND INTO EARLY NEXT WEEK...

SYNOPSIS...
Tropical Depression Harvey is located as of 4 PM CDT about 460 to
500 miles southeast of the Middle Texas coast. The system has not
really strengthened or move much during the day.

Meanwhile, a TUTT low is over the forecast area and is becoming
more elongated today, while a surface front moves into Northern
Louisiana and Northeast Texas. With the weakness aloft and a moist
unstable air mass in place, scattered showers and thunderstorms
are developing and moving from the northeast to the southwest.
Some of the storms could produce brief gusty winds and frequent
cloud to ground lightning before they diminish after sunset.

Rua

DISCUSSION...
High confidence in the short term. The surface front will continue
to sag a little to the south toward the coast. Meanwhile, the TUTT
will continue to weaken. The weakness aloft, combined with the
frontal boundary and the general summertime unstable and moist air
mass will continue to see the daytime scattered showers and
thunderstorms that will decrease after sunset. This weather
pattern should hold through Friday.

There is a moderate confidence in the mid range forecast. This
part of the forecast will depend on the track and strength of
tropical cyclone Harvey, and will closely follow the official
forecast from the National Hurricane Center.

Based on this, tropical storm force winds should stay out of the
forecast area. Some surge issues could arise and this will be
watched closely. Right now we are looking at 1 to 3 feet above
predicted values for Friday Night into Saturday Night west of
Cameron to High Island, and 1 to 2 feet east of Cameron to the
Lower Atchafalaya River. Values beyond this will be either higher
or lower depending again on the strength and track of Harvey.

The higher tropical like moisture will being to move into the
forecast area during the day on Saturday and continue through
Monday, as Harvey loses and steering currents and meanders around
the mid Texas coast, with Precipitable Water Values over 2.5
inches and Mean RH over 90 percent pushed in by a deep south flow.
So, with tropical moisture forced over the old frontal boundary,
some of these precipitation efficient showers will focused with
even maybe some training rainbands. Therefore, heavy rainfall has
been included in the weather grids starting on Saturday. If these
conditions still are looking like this on Thursday, then a Flash
Flood Watch may be issued at that time for the Saturday and beyond
period.

One other note is a low tornado threat depending on how the outer
rainbands set up late Friday into Saturday.

There is lower confidence in the extended portion of the forecast.
Harvey may become trapped between an upper level ridge over the
Southwest US and the Sub-tropical Ridge building across South
Florida into the Gulf. Biggest question will be if a short wave
trough dripping down from the Central Plains early next week, can
pick up the system and move it off to the east, and if the surface
low center can emerge any over the Gulf of Mexico. At this point,
solutions diverge enough to keep high range chances in the
forecast through Wednesday.

Rua

MARINE...
The forecast for the coastal waters will highly depend on the
eventual track and strength of Tropical Depression Harvey. At
this time, no tropical storm force winds are anticipated for the
coastal waters and thus no watches are in effect at this time.
Elevated winds and seas could start to reach the coastal waters
late Friday into Saturday. Also, showers and storms will be on the
increase at that time.

Rua

HYDROLOGY...
With a slow moving tropical system interacting with a surface
boundary, there is a potential for very heavy rainfall that could
lead to flooding. Looks like the heaviest rainfall could start
during the day on Saturday and continue into early next week.
Storm rainfall totals area wide through Wednesday Morning will
average 10 to 15 inches with locally 20 inches across Southwest
Louisiana into Southeast Texas. The totals across Central
Louisiana and South Central Louisiana look like 6 to 12 inches
with locally 16 inches.

Currently, river flood warnings are out for portions of the Lower
Calcasieu River at points Salt Water Barrier and Old Town Bay.
These initial warnings are for the higher tides along the coast
backing water up the channel taking these levels into minor flood
stage. A reminder, these levels do not include the potential
rainfall amounts forecast over the weekend.

Rua

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  73  89  72  86 /  30  50  20  50
LCH  75  91  76  86 /  30  50  40  60
LFT  75  91  76  87 /  30  50  40  60
BPT  76  90  76  85 /  20  40  50  60

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...None.
GM...None.
&&

$$


AVIATION...05



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