re: Harvey ***Catastrophic Flooding Event***

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Area Forecast Discussion
National Weather Service New Orleans LA
419 AM CDT Wed Aug 23 2017

.SHORT TERM...
Remnants of Harvey beginning to look better this morning. This
system could be the result of a prolonged rainfall event for not
just our area but the entire western half of the gulf coast states.
NHC is giving this system a 90% chance of developing into a tropical
cyclone in 48 hours. And a tropical depression or storm is very
likely to form today. The next thing to look at that will play a
part in what is to come will be the synoptic trough located over
southern Arkansas and northern Mississippi this morning. This trough
will continue to sink southward and stall near the gulf coast. This
trough is also what is causing the weakness in the mid-upper level
ridging that was over the area yesterday. As the tropical system
moves northwest, very deep tropical moisture will be forced
northward on its east side into the stalled trough where plenty of
lift will cause an elongated area of sh/ts to break out initiating
from the tropical cyclone over southeast Texas to the Florida
panhandle. This should begin to be observe Friday or Friday night.
This scenario is expected to continue through the weekend into the
new week as well with rainfall rates slowly increasing over the
weekend into the new week. The tropical feature should slow or even
stall possibly just inland over southeast Texas before getting
picked up in the westerlies starting Sunday night or Monday. As the
low begins to lift, it will do so along the synoptic trough
boundary. Where this boundary is located by Monday should be the
area of heaviest rainfall where it interacts with the low.

The systems exit scenario can not be resolved with any confident
accuracy at the moment since the energy that will pick this
tropical feature up is still located over the Pacific. But the
system that does finally pick it up should begin to be sampled
with the RAOB network by Friday. This will cause the global models
to come into much stronger agreement with respect to the systems
exit. But regardless of naming or any other nomenclature, this
system will have the potential to produce very heavy flooding
rainfall and gusty winds over the entire area as well as high
tides especially west of the Mississippi River. Another
possibility associated with this event will be waterspouts and
tornadic thunderstorms on the east side of the system within the
banding structures. This may depend on how close the low
eventually comes to the area though.

DSS code: Yellow.
Deployed: NOHSEP.
Activation: None.
Activities: DSS support for NOHSEP; Monitoring Convective and
tropical trends.

Decision Support Services (DSS) Code Legend
Green = No weather impacts that require action.
Blue = Long-fused watch, warning, or advisory in effect or
high visibility event.
Yellow = Heightened impacts with short-fused watch, warning or
advisory issuances; radar support.
Orange = High Impacts; Slight to Moderate risk severe; nearby tropical
events; HazMat or other large episodes.
Red = Full engagement for Moderate risk of severe and/or
direct tropical threats; Events of National Significance.

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