Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS64 KLCH 222323
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
623 PM CDT Tue Aug 22 2017

.AVIATION...Showers and storms continue to decrease across the
area this evening, however patchy -ra will remain in place for the
next hour or two. Additional storms are expected tomorrow as
diurnal heating occurs. Mostly VFR conditions are still expected.


&&

.PREV DISCUSSION... /issued 446 PM CDT Tue Aug 22 2017/ 

DISCUSSION...
Latest water vapor satellite imagery showed the upper low over the
NW Gulf starting to elongate/weaken, while a robust upper trof
swings into the NE CONUS, eroding the SE CONUS ridge. To the
south, the remnants of Harvey are just beginning to exit the NW
Yucatan Peninsula and enter the southern Gulf.

Radar imagery continues to show scattered showers and
thunderstorms ongoing over a good part of Louisiana along and
north of I-10. Though aided by the upper low, this activity is
largely driven by diurnal instability, and should come to an end
over the next few hours. After a relatively quiet overnight
period, another day of scattered showers and thunderstorms is on
tap for tomorrow as the weak upper low/trof remains over the NW
Gulf. In addition, by late tomorrow, the trof digging into the 
ERN CONUS will send a weak frontal boundary toward and eventually 
into the forecast area, providing an additional focus for shower
and thunderstorm development that will likely persist WED night
and on into THU.

Meanwhile, to the south, the remnants of Harvey are expected to
regenerate into a tropical cyclone by tomorrow, with the system
subsequently strengthening and tracking TWD the NW. Current model
consensus is for the system to come ashore the lower to middle TX
coast region late FRI. An inverted trof axis extending N of 
Harvey, along with an influx of associated tropical moisture, will
begin to result in widespread rainfall spreading into the area on
FRI, which could be the onset of a significant rainfall event for
the area pending the eventual strength/track of the system. While
model divergence increases post-landfall, there is broad consensus
for a near stall or at least slow NWD movement over S Central TX 
through the weekend, with a subsequent ejection EWD early next 
week. The gridded forecast was constructed based on this consensus,
and thus does not represent either the worst or best case scenario
for the area. 

Based on this consensus, a prolonged and potentially heavy 
rainfall event is forecast over the weekend and into early next 
week. Event total 6 to 8 inches of rainfall are possible over E 
TX and parts of SW LA, with 4 to 6 inches over Central and South 
Central LA. In addition, due to the persistent period of moderate 
to potentially strong onshore flow, a prolonged period of coastal 
flooding is possible.

It cannot be stressed strongly enough that while confidence has
increased since this time yesterday, there remains a high degree
of uncertainty regarding the eventual path and strength of this
system, and thus its resultant impacts. Please stay tuned to
subsequent forecasts from this office and the NHC.

13 

MARINE...
Light southeast winds and low seas will continue through
Wednesday as surface high pressure ridges west across the Gulf
States. Scattered showers and thunderstorms are expected each
afternoon. The high is forecast to breakdown late Wednesday as 
the region is squeezed between an approaching cold front to the 
north and what is likely to be a regenerated Harvey over the 
Southern Gulf of Mexico. Elevated winds and seas are expected to 
begin affecting the coastal waters on Friday, and continue through
the weekend. The magnitude of these elevated winds and seas, and
their duration, will depend on the eventual track and strength of
the system. At this time, there is a broad consensus for the 
tropical cyclone to come ashore the lower to middle Texas coast 
late Friday, then subsequently slow down over South Central Texas
over the weekend before turning eastward early next week. Should 
this come to fruition, a prolonged period of rainfall, gusty 
onshore flow, and rough seas will result. 

13

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  73  91  73  88 /  10  50  30  40 
LCH  77  92  77  90 /  10  40  30  50 
LFT  77  92  76  90 /  10  40  30  50 
BPT  75  91  75  89 /  10  40  20  40 

&&

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

National Weather Service Glossary of Abbreviations