[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 020843
TCDAT4

TROPICAL STORM HERMINE DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
500 AM EDT FRI SEP 02 2016

Hermine made landfall near St. Marks, Florida, around 0530 UTC with
70-kt winds. Since that time radar data and surface observations
indicate that the center has continued to move inland. The radar
presentation has deteriorated, and it is estimated that Hermine
has weakened to tropical storm status with 60-kt winds. Additional
weakening is anticipated while the cyclone moves farther inland, but
it could reinvigorate as an extratropical cyclone when it moves
over water and interacts with a baroclinic trough in about 48 hours.

The best estimate of the initial motion 025/12 kt. Hermine is
embedded within the southwesterly flow ahead of a mid-latitude
trough, and this flow pattern should steer the cyclone toward the
northeast with an increase in forward speed during the next day
or two. Track models are in very good agreement during this
period. After that time, when Hermine begins to interact with
a baroclinic trough, the cyclone should slow down significantly
and begin to meander. On days 3-5, the track guidance becomes rather
divergent, decreasing confidence in the forecast.  The NHC
prediction keeps an extratropical cyclone moving little or drifting
northward a few hundred miles off the northeastern U.S coast during
that time. There is a possibility that the system could regain some
tropical characteristics in 4-5 days, but this remains uncertain as
indicated in the previous NHC forecast.

KEY MESSAGE:

1. Hermine is expected to become a post-tropical cyclone while
still producing hazardous winds and storm surge over land.  NWS
policy allows NHC to write advisories on and issue tropical storm
watches and warnings for post-tropical cyclones, when the system
continues to pose a significant threat to life and property. NHC and
the NWS Eastern Region have decided that this option will be invoked
for Hermine.  After Hermine becomes a post-tropical cyclone, NHC
will continue to issue its full suite of advisory and warning
products for as long as the system remains a significant threat to
land.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 30.8N  83.6W   60 KT  70 MPH
 12H  02/1800Z 32.5N  81.4W   45 KT  50 MPH...INLAND
 24H  03/0600Z 34.5N  77.9W   40 KT  45 MPH...INLAND
 36H  03/1800Z 36.0N  74.5W   40 KT  45 MPH...OVER WATER
 48H  04/0600Z 37.0N  72.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  05/0600Z 38.0N  72.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  06/0600Z 38.5N  72.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  07/0600Z 39.0N  72.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Avila
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