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TROPICAL STORM OLAF DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192015
800 PM PDT FRI OCT 16 2015

The cloud pattern of Tropical Depression Nineteen-E has continued
to become better organized during the past several hours.  There
is now a persistent convective area near the center and ragged
outer bands in the western semicircle.  Satellite intensity
estimates have increased to 45 kt from SAB and 35 kt from TAFB.  In
addition, Rapidscat data from the International Space Station showed
an area of 30-35 kt winds just north of the central convection.
Based on these data, the depression is upgraded to Tropical Storm
Olaf with 35 kt winds.

The initial motion estimate is now 270/12.  Olaf is currently being
steered by a mid-level subtropical ridge.  The dynamical models
forecast the ridge to persist but weaken during the next 72-96
hours due to the influence of a strong deep-layer trough forecast
to develop over the southwestern United States.  This evolution
should cause Olaf to continue westward with a decrease in forward
speed during the first 36-48 hours, followed by a west-northwestward
motion from 48-96 hours. After that time, the ridge is forecast to
break to the east of the Hawaiian Islands, which should allow the
storm to turn more northward.  The track guidance is generally in
good agreement with this scenario, with the ECMWF, GFS, and the
various consensus models rather tightly clustered.  The new
forecast track is similar to the previous track through 72 hours,
then is nudged slightly westward thereafter.  The new track is
close to the model consensus.

Olaf is expected to remain in an environment of good moisture,
light shear, and warm sea surface temperatures for at least the
next three days, so there is no obvious reason it should not
strengthen.  On one side of the guidance, the LGEM forecasts Olaf
to become a major hurricane in 72 hours, and the Rapid
Intensification Index of the SHIPS model shows a 30-35 percent
chance of 30 kt of strengthening during the next 24 hours.  On the
other side, the GFDL and HWRF forecast a much slower rate of
intensification. The new intensity forecast is nudged upward from
the previous forecast based on current trends and is a compromise
between the SHIPS model and the Florida State Superensemble.  As
stated in the previous advisory, given the very conducive
large-scale environment, it would not be surprising to see more
strengthening than is currently forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  17/0300Z  9.7N 127.6W   35 KT  40 MPH
 12H  17/1200Z  9.7N 129.1W   45 KT  50 MPH
 24H  18/0000Z  9.7N 130.8W   55 KT  65 MPH
 36H  18/1200Z 10.0N 132.4W   65 KT  75 MPH
 48H  19/0000Z 10.5N 133.9W   75 KT  85 MPH
 72H  20/0000Z 12.0N 137.0W   95 KT 110 MPH
 96H  21/0000Z 14.0N 140.0W   95 KT 110 MPH
120H  22/0000Z 16.5N 141.5W   90 KT 105 MPH

$$
Forecaster Beven

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