ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM

TROPICAL STORM OLAF DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192015
800 PM PDT SAT OCT 17 2015

After the pause noted in the previous advisory, Olaf has resumed
intensification this evening.  Well-defined convective bands
with cloud tops colder than -80C have formed around the center, and
microwave data show a developing 15 n mi wide eye.  Satellite
intensity estimates have increased to 55 kt from TAFB and SAB, and
there is a recent CIMSS AMSU intensity estimate of 52 kt.  Based on
these data, the initial intensity is increased to 55 kt.

The initial motion is 270/8.  Olaf is now moving slower as the
subtropical ridge to the north weakens in response to the influence
of a mid- to upper-level trough near the U. S. west coast.  A
general west-northwestward motion is expected for the next two days
or so as the cyclone moves on the south side of the weakened ridge.
After that time, a second mid- to upper-level trough passing north
of the Hawaiian Islands is forecast to cause a break in the ridge,
allowing Olaf to turn northwestward by 72 hours and northward by
120 hours. There is little overall change in the guidance since the
last advisory.  Thus, the new forecast track is very similar to the
previous track and lies near the center of the track guidance
envelope.

There is still some light northwesterly shear over Olaf.  However,
this is forecast to diminish during the next 24 hours, and improving
cirrus outflow suggests this may already be occurring.  Based on
this, warm sea surface temperatures, and a moist environment,
continued strengthening is expected during the next 48 hours.
After 72 hours, developing southerly shear and dry air entrainment
are expected to cause Olaf to weaken.  The new intensity forecast
is similar to the previous forecast and is in best agreement with
the Florida State Superensemble.  It should be noted that the small
inner core seen in microwave imagery could allow rapid
intensification, and the Rapid Intensification Index of the SHIPS
model has a 25-30 percent chance of a 30-kt increase in intensity
during the next 24 hours.  Should this occur, Olaf could get
significantly stronger than currently forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z  9.2N 131.0W   55 KT  65 MPH
 12H  18/1200Z  9.4N 132.3W   65 KT  75 MPH
 24H  19/0000Z  9.9N 134.1W   80 KT  90 MPH
 36H  19/1200Z 10.4N 135.8W   90 KT 105 MPH
 48H  20/0000Z 11.2N 137.4W  100 KT 115 MPH
 72H  21/0000Z 13.5N 140.5W  100 KT 115 MPH
 96H  22/0000Z 15.5N 142.0W   95 KT 110 MPH
120H  23/0000Z 18.0N 142.5W   80 KT  90 MPH

$$
Forecaster Beven

NNNN