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HURRICANE OLAF DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192015
800 PM PDT MON OCT 19 2015

Olaf has maintained a small pinhole eye with a diameter of no more
than 10 n mi. Satellite intensity estimates were a consensus
T6.0/115 kt from TAFB, UW-CIMSS ADT, and the NHC AODT algorithm at
20/0000Z. However, since that time the eye has warmed a little and a
ring of cloud tops colder than -75C has developed around the eye, so
the intensity has been nudged slightly higher to 120 kt.

The initial motion estimate is 275/09 kt. Olaf is expected to
continue moving westward to west-northwestward along the southern
periphery of a deep-layer ridge for the next 24 hours or so, and
then turn northwestward toward a developing weakness in the ridge on
days 2 and 3. By 96 and 120 hours, a series of fast-moving shortwave
troughs embedded in the mid-latitude westerlies is expected to
gradually create a break in the mid-level ridge between 145W-150W
longitude, allowing Olaf to move northward and remain well east of
the Hawaiian Islands. The latest NHC model guidance is in much
better agreement on this developing scenario compared to 24 hours
ago, and even the UKMET model has shifted eastward and is now on
the east side of the guidance envelope at 96 and 120 hours. The
official forecast track lies a little to the left of the previous
advisory track, and follows the consensus models TVCE and GFEX.

There has been slight flattening of the CDO in the northwestern
quadrant caused by some light to moderate northwesterly mid-level
shear as noted in recent UW-CIMSS shear analyses, which could
inhibit intensification some in the short term. However, some
additional strengthening is still likely over the next day or so
since Olaf will be affected by deep-layer shear of 5 kt or less and
be over 29C SSTs. As mentioned in the previous advisory, there could
be fluctuations in intensity due to eyewall replacement cycles that
can not be forecast more than a few hours in advance. The NHC
intensity forecast continues to indicate a peak of 125 kt at 12-36
hours, followed by a slow decay by 48-72 as Olaf begins to move
slowly over slightly cooler SSTs and into a moderate southwesterly
vertical wind shear regime. The official intensity forecast remains
above the intensity consensus, but below the LGEM and SHIPS
forecasts, which bring Olaf to just below category 5 strength in
36-48 hours.

With Olaf moving into the central North Pacific basin within the
next six hours or so, this will be the last advisory from NHC.
Future information on Olaf can be found in advisories issued by the
Central Pacific Hurricane Center beginning at 1100 PM HST (0900Z).

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 10.1N 139.5W  120 KT 140 MPH
 12H  20/1200Z 10.4N 140.8W  125 KT 145 MPH
 24H  21/0000Z 11.1N 142.4W  125 KT 145 MPH
 36H  21/1200Z 12.0N 143.8W  125 KT 145 MPH
 48H  22/0000Z 13.0N 145.0W  120 KT 140 MPH
 72H  23/0000Z 15.4N 146.6W  105 KT 120 MPH
 96H  24/0000Z 18.3N 146.9W   95 KT 110 MPH
120H  25/0000Z 20.9N 146.4W   80 KT  90 MPH

$$
Forecaster Stewart

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