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HURRICANE OLAF DISCUSSION NUMBER  16
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192015
200 PM PDT SUN OCT 18 2015

Olaf hasn't changed much in organization during the past few hours,
with satellite imagery still showing a CDO and a large, but broken,
convective band in the western and southern semicircles of the
cyclone. There appears to be a dry slot working into the western
side of the circulation, and the eye has been less distinct in
recent microwave imagery than it was earlier. The initial intensity
remains 70 kt, a little higher than the latest Dvorak estimates from
TAFB, SAB, and the UW-CIMSS ADT. The initial 34- and 50-kt wind
radii were adjusted based on a timely 1815Z ASCAT-B overpass.

The pause in strengthening could be due to the aforementioned dry
air and moderate west-northwesterly to northwesterly shear analyzed
over the cyclone by the SHIPS model and UW-CIMSS. Given the shear
and an inner-core that may be a little less organized, the new NHC
intensity forecast shows a slower rate of strengthening in the first
couple of days, and is now closer to the bulk of the intensity
guidance. The forecast still shows Olaf becoming a major hurricane
in 2-3 days followed by a slow decay as the hurricane moves over
somewhat cooler SSTs late in the period. The NHC prediction is close
to the SHIPS model through much of the period, but a little above it
at peak intensity.

Olaf continues to move quickly westward, with a motion now estimated
at 280/12. This continues a trend of the hurricane moving faster and
to the left of the previous couple of forecasts. While the
subtropical ridge to the north weakens is still expected to weaken
and lift northward, the track model guidance continues to shift
westward given the initial motion and Olaf failing to gain as much
latitude as previously thought in the short term. The new NHC track
forecast has been adjusted to the left of the previous one,
especially at days 3 through 5, and is now close to a blend of the
latest ECMWF and GFS forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z  9.7N 134.3W   70 KT  80 MPH
 12H  19/0600Z  9.9N 135.7W   75 KT  85 MPH
 24H  19/1800Z 10.3N 137.5W   85 KT 100 MPH
 36H  20/0600Z 11.0N 139.1W   95 KT 110 MPH
 48H  20/1800Z 11.8N 140.6W  105 KT 120 MPH
 72H  21/1800Z 13.7N 143.4W  105 KT 120 MPH
 96H  22/1800Z 16.0N 145.0W   95 KT 110 MPH
120H  23/1800Z 18.0N 145.0W   85 KT 100 MPH

$$
Forecaster Brennan

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