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Tropical Storm Helene Discussion Number   3
NWS National Hurricane Center Miami FL       AL082018
1100 PM AST Fri Sep 07 2018

A very timely ASCAT pass indicated that the winds associated with
the depression have increased to 35 kt, and also that the center was
a little east of the location previously indicated. This is very
common in systems during the formative stage.  Based on the ASCAT
data, the system has been upgraded to Tropical Storm Helene, the
eighth named storm of the season. The satellite presentation has
also improved during the past several hours, and now the cyclone has
large cyclonically curved convective bands to the south of the
center. The outflow is fair in all quadrants.

Helene will be moving over warm waters and within an environment
of light shear through the next 3 to 4 days, and most of the
guidance responds to that environment by gradually strengthening the
cyclone. The NHC forecast follows the trend of the intensity
consensus, and brings Helene to hurricane intensity in about 3 days.

Currently, Helene is embedded within a southwest monsoon-type flow,
and is moving toward the west at about 9 or 10 knots. However, as
the cyclone moves away from the African coast, it will become
steered by the easterly flow around the subtropical ridge and should
then increase in forward speed. Most of the track models are in
extremely good agreement, at least for the next 3 days when the
confidence in the forecast is high. At the long range, a mid-level
trough is expected to develop over the central Atlantic, forcing the
cyclone to turn more to the northwest and even north later on. The
NHC forecast is in the middle of the guidance envelope and basically
on top of the corrected consensus HCCA.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 13.6N  18.5W   35 KT  40 MPH
 12H  08/1200Z 13.8N  19.9W   35 KT  40 MPH
 24H  09/0000Z 14.3N  22.3W   40 KT  45 MPH
 36H  09/1200Z 14.8N  25.0W   50 KT  60 MPH
 48H  10/0000Z 15.4N  28.0W   55 KT  65 MPH
 72H  11/0000Z 17.0N  33.9W   65 KT  75 MPH
 96H  12/0000Z 18.5N  39.0W   65 KT  75 MPH
120H  13/0000Z 20.5N  42.5W   60 KT  70 MPH

$$
Forecaster Avila

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