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Tropical Storm Helene Discussion Number  27
NWS National Hurricane Center Miami FL       AL082018
1100 PM AST Thu Sep 13 2018

Helene's cloud pattern is beginning to have the appearance of a
cyclone in extratropical transition with the rain shield limited to
the northwest quadrant.  The Dvorak numbers have decreased, but very
recent scatterometer data show winds of around 55 kt associated with
Helene's circulation, and this is the intensity value used in this
advisory. Most of the guidance suggests that Helene's strength
should remain steady through the forecast period, perhaps due to
baroclinic forcing. On this basis, the NHC forecast keeps Helene
with the same intensity through the forecast period, but as a
post-tropical cyclone beyond 3 days.

Helene has increased its forward speed and is now moving toward the
north or 010 degrees at about 18 kt.  The flow ahead of a sharp
mid-level trough is well established, and this pattern will continue
to steer Helene toward the north and then northeast during the next
few days. This is consistent with most of the track guidance which
is indeed tightly clustered.  The NHC forecast is not very different
from the previous one, and is in between the corrected consensus
HCCA and the multi-model consensus aids.

Given the increase in forward speed and the expansion of the wind
field, a tropical storm warning will likely be required for a
portion of the Azores early Friday.

FORECAST POSITIONS AND MAX WINDS

INIT  14/0300Z 28.6N  36.5W   55 KT  65 MPH
 12H  14/1200Z 31.4N  35.9W   55 KT  65 MPH
 24H  15/0000Z 34.8N  34.7W   50 KT  60 MPH
 36H  15/1200Z 37.8N  32.8W   50 KT  60 MPH
 48H  16/0000Z 40.0N  29.0W   50 KT  60 MPH
 72H  17/0000Z 43.0N  21.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  18/0000Z 46.5N  15.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  19/0000Z 53.0N   5.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Avila

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