Hurricane Helene Discussion Number  12
NWS National Hurricane Center Miami FL       AL082018
500 AM AST Mon Sep 10 2018

Little change in the Helene's cloud pattern has been observed
during the past 6 hours.  The earlier mentioned ragged banding-type
eye feature is still apparent in the enhanced infrared BD-curve
imagery and a recent SSMI/S microwave overpass.  The initial
intensity is held at 75 kt, and is based on the subjective Dvorak
intensity estimates.

Helene is moving within a fairly ripe environment and over warm
oceanic sea surface temperatures.  These conducive conditions
should promote additional strengthening over the next 36 hours.
Afterward, increasing south-southwesterly shear, lower
mid-tropospheric moisture, and cooler water are expected to induce
weakening, however gradually, through day 5.  The official forecast
follows suit and is similar to the better performing IVCN intensity
consensus model.

Helene's initial motion is estimated to be west-northwestward, or
285/15 kt, and this general motion is forecast during the next 48
hours.  Beyond that period, a break in the subtropical ridge to the
northwest of Paul, created by a mid- to upper-level cut-off low
digging southward, should induce a northward turn with a gradual
increase in forward motion.  The large-scale models all indicate
this change in the synoptic steering pattern, although there is some
disparity on how soon Helene will turn toward the north.  The NHC
track is quite close to the previous forecast and lies between the
consensus guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  10/0900Z 14.3N  28.9W   75 KT  85 MPH
12H  10/1800Z 14.8N  30.9W   80 KT  90 MPH
24H  11/0600Z 15.5N  33.4W   85 KT 100 MPH
36H  11/1800Z 16.3N  35.6W   85 KT 100 MPH
48H  12/0600Z 17.2N  37.2W   80 KT  90 MPH
72H  13/0600Z 20.3N  39.4W   65 KT  75 MPH
96H  14/0600Z 25.3N  40.8W   55 KT  65 MPH
120H  15/0600Z 31.2N  41.1W   50 KT  60 MPH

$$
Forecaster Roberts