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Tropical Storm Helene Discussion Number   8
NWS National Hurricane Center Miami FL       AL082018
500 AM AST Sun Sep 09 2018

Satellite imagery indicates that Helene continues to become better
organized with an increase in banding overnight.  A couple of
recent microwave images show that the inner core continues to
organize with a low-level ring evident and indication that a
banding-type eye is forming.  Dvorak satellite T-numbers have
increased and support an initial intensity of 55 kt.

Helene is forecast to remain over SSTs of 27-28C during the next
couple of days.  The upper-level wind pattern is also expected to
be quite favorable, and these conditions should support steady
intensification.  Slightly cooler waters and increasing
southwesterly shear from an upper-level trough to the northwest of
Helene are likely to put an end to the intensification process by
day 3. After that time, Helene is forecast to move closer to the
aforementioned trough with southwesterly shear and drier mid-level
air likely to result in weakening by day 4 and 5.  The NHC intensity
forecast is near the IVCN intensity consensus model, but it is a
little more conservative than the FSSE and HCCA models.

The tropical storm is moving westward or 270 degrees at 12 kt. A
deep-layer ridge to the north of the storm should steer Helene
westward to west-northwestward during the next couple of days.  By
mid-week, Helene is expected to approach a weakness in the ridge
between 40-50W longitude and the cyclone is predicted to turn
northwestward, then north-northwestward by the end of the period.
The track guidance is in fairly good agreement on this scenario,
but there is some spread later in the period as to exactly what
longitude the northwesterly turn takes place.  The NHC forecast is
between the various dynamical model solutions and is close to the
HFIP corrected consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  09/0900Z 13.2N  24.0W   55 KT  65 MPH
 12H  09/1800Z 13.4N  26.0W   65 KT  75 MPH
 24H  10/0600Z 14.0N  28.9W   75 KT  85 MPH
 36H  10/1800Z 14.7N  31.9W   85 KT 100 MPH
 48H  11/0600Z 15.4N  34.5W   90 KT 105 MPH
 72H  12/0600Z 17.4N  38.3W   80 KT  90 MPH
 96H  13/0600Z 20.5N  41.0W   65 KT  75 MPH
120H  14/0600Z 25.0N  42.5W   50 KT  60 MPH

$$
Forecaster Brown

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