[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 010258
TCDAT4

TROPICAL STORM HERMINE DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
1000 PM CDT WED AUG 31 2016

Data from NOAA and Air Force Reserve Hurricane Hunter aircraft this
afternoon and evening indicate that Hermine has continued to
strengthen, based on maximum 850-mb flight-level winds of 57 kt and
peak SFMR surface winds of 52 kt. A recent dropsonde in the center
of Hermine measured a pressure of about 998 mb, which is a decrease
of 6 mb from the previous advisory.

Recon fixes over the past 4 hours indicate that the estimated motion
is north-northeastward or 025/09 kt. An approaching mid-tropospheric
trough located over the southeastern United States and extending
southward into the north-central Gulf of Mexico is expected to
gradually lift out Hermine to the north-northeast tonight and
Thursday, and then northeastward after 24 hours. The NHC model is
in very good agreement on this developing steering flow pattern.
Later in the forecast period, significant uncertainty in the track
forecast remains, depending on how much the post-tropical cyclone
interacts with a mid-latitude cutoff low that develops over the
northeastern United States. The new NHC forecast track has been
shifted slightly to the east of the previous advisory track,
primarily due to the more eastward initial position determined from
recent recon fixes, and lies just to the left of the consensus model
TVCN.

The vertical wind shear is forecast by the GFS and the ECMWF models
to shift from the current west-northwesterly direction to
southwesterly by 18-24 hours at about 5 to 10 kt. SSTs are expected
to be near 30C.  The intensity consensus IVCN again brings Hermine
to hurricane strength prior to landfall and the offical forecast
follows this guidance, forcing the issuance of a hurricane warning
with this advisory.  The predicted extratropical transition of the
system is based on the global model guidance, which show the cyclone
becoming embedded within a frontal zone over the eastern United
States by 72 hours.


FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 25.8N  87.0W   50 KT  60 MPH
 12H  01/1200Z 26.9N  86.4W   55 KT  65 MPH
 24H  02/0000Z 28.7N  85.4W   65 KT  75 MPH
 36H  02/1200Z 30.7N  83.8W   60 KT  70 MPH...INLAND
 48H  03/0000Z 32.8N  81.4W   45 KT  50 MPH...INLAND
 72H  04/0000Z 37.0N  76.3W   40 KT  45 MPH...POST-TROP/INLAND
 96H  05/0000Z 39.0N  74.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  06/0000Z 39.0N  71.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart
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