Hurricane Helene Discussion Number  21
NWS National Hurricane Center Miami FL       AL082018
1100 AM AST Wed Sep 12 2018

The eye has become less distinct, but the overall convective pattern
remains well organized and symmetric. Based on the latest Dvorak
estimates, the initial intensity is kept at 80 kt. Most of the
guidance show a significant increase in the shear in 24 hours,
but the SSTs are not changing much for the next 2 days or so, thus
gradual weakening is forecast.  After that time, both shear and SSTs
will become belligerently unfavorable, resulting in additional
weakening. By the end of the forecast period, Helene should have
acquired extratropical characteristic.

The hurricane is moving toward the north-northwest or 340 degrees
at 12 kt, embedded in the southerly flow to the east of the digging
trough over the central Atlantic.  Since the trough is forecast to
amplify, Helene will be forced to turn to the north-northeast and
northeast with an increase in forward speed. The global models
remain in fairly good agreement on the current forecast track of
Helene, and they all bring the cyclone near the Azores in 3 or 4
days. Interests in those islands should closely monitor the progress
of Helene over the next several days.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 20.3N  36.5W   80 KT  90 MPH
12H  13/0000Z 22.0N  37.2W   70 KT  80 MPH
24H  13/1200Z 24.5N  37.5W   65 KT  75 MPH
36H  14/0000Z 27.5N  37.2W   60 KT  70 MPH
48H  14/1200Z 31.0N  36.5W   50 KT  60 MPH
72H  15/1200Z 37.7N  33.2W   45 KT  50 MPH
96H  16/1200Z 42.5N  26.0W   45 KT  50 MPH
120H  17/1200Z 47.5N  17.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Avila