[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 012045
TCDAT4

HURRICANE HERMINE DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
400 PM CDT THU SEP 01 2016

Hermine was recently upgraded to a hurricane based on an
SFMR-observed surface wind from an Air Force Hurricane Hunter
aircraft.  The initial intensity is set at 65 kt based on that
observation.  Satellite images show that the cloud pattern continues
to gradually become better organized with more distinct curved bands
of showers and thunderstorms, although the system currently lacks
concentrated inner-core convection.  Hermine has a little more time
to strengthen, so the official forecast shows a slight additional
increase in intensity before landfall.  This is consistent with the
latest LGEM guidance.  Hermine is forecast to become extratropical
at 48 hours when the global models forecast it to become embedded
within a frontal zone.  Later in the forecast period,
vertical shear decreases and the cyclone could be situated over
marginally warm waters.  Therefore there is the possibility of the
system regaining some tropical characteristics in 4-5 days, although
this is speculative at this time.

Aircraft center fixes indicate that the motion remains 030/12 kt.
The flow on the eastern side of a mid-level trough over the
southeastern United States should cause Hermine to move
north-northeastward to northeastward with some increase in forward
speed during the next day so.  By 48 hours, the track guidance
shows the system slowing down as it begins to interact with a
mid-level cutoff vortex over the eastern United States.  In 3 days
or so, the post-tropical cyclone merges with the cutoff low and a
further slowing down of the motion is expected.  The official track
forecast lies between the latest GFS and ECMWF predictions.

KEY MESSAGES:

1. As landfall nears, it is important to not focus on the exact
forecast track.  Hermine is an extremely asymmetric storm, with a
large extent of dangerous winds, life-threatening storm surge, and
flooding rains well to the east and southeast of the path of the
center.

2. 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  01/2100Z 28.5N  85.0W   65 KT  75 MPH
 12H  02/0600Z 30.2N  83.9W   70 KT  80 MPH
 24H  02/1800Z 32.4N  81.6W   50 KT  60 MPH...INLAND
 36H  03/0600Z 34.5N  78.2W   45 KT  50 MPH...INLAND
 48H  03/1800Z 36.3N  75.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  04/1800Z 38.0N  72.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  05/1800Z 38.5N  71.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  06/1800Z 39.5N  70.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch

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