[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 011500
TCDAT4

TROPICAL STORM HERMINE DISCUSSION NUMBER  16
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
1000 AM CDT THU SEP 01 2016

Hermine is gradually becoming better organized, with convective
banding developing over the eastern semicircle of the circulation.
Upper-level outflow continues to be restricted to the northwest of
the storm by a cyclonic shear axis depicted by water vapor
imagery.  The current intensity is set at 55 kt in agreement with
SFMR-observed surface winds from an Air Force Hurricane Hunter
aircraft.  The intensity forecast continues to show Hermine becoming
a hurricane before landfall which is in general agreement with the
numerical guidance.  The global models show Hermine embedded within
a frontal zone by 48 hours, so the forecast shows the system
becoming extratropical at that time.  There is some concern about
the evolution of the post-tropical cyclone later in the forecast
period, since the shear starts decreasing after 72 hours.  This
could allow the system to reacquire some tropical characteristics in
4-5 days, although it is not certain how close to the coast the
cyclone will be by that time.

Based on Hurricane Hunter aircraft fixes and a dropsonde from the
NASA Global Hawk aircraft, the initial motion is estimated to be
030/12 kt.  A mid-tropospheric trough should steer the system
north-northeastward to northeastward for the next couple of days.
Later in the forecast period, a developing mid-level cutoff low near
the northeast United States coast will cause a slowing of the
forward speed as the cyclone interacts with the low.  The official
forecast track is essentially a blend of the latest GFS and ECMWF
solutions, with the former model showing a track closer to the
northeast coast and the latter taking the system farther offshore.

KEY MESSAGES:

1. It is important to not focus on the exact forecast track.
Hermine is a rather 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 undergo a complex interaction with a
frontal system when it reaches the Carolinas over the weekend.  It
is a little early to say what the specific impacts will be for the
mid-Atlantic and northeastern states.


FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 27.4N  86.0W   55 KT  65 MPH
 12H  02/0000Z 29.0N  84.8W   65 KT  75 MPH
 24H  02/1200Z 31.1N  82.9W   50 KT  60 MPH...INLAND
 36H  03/0000Z 33.1N  80.0W   45 KT  50 MPH...INLAND
 48H  03/1200Z 35.2N  76.7W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  04/1200Z 38.0N  72.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  05/1200Z 38.5N  71.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  06/1200Z 39.5N  70.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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