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Hurricane Olivia Discussion Number  24
NWS National Hurricane Center Miami FL       EP172018
800 AM PDT Thu Sep 06 2018

Satellite imagery indicates that Olivia has a well-defined 20 n mi
wide eye, although the eye is not quite as distinct as it was at
the time of the previous special advisory.  The eye is inside of a
central dense overcast with eyewall cloud tops as cold as -80C.
Satellite intensity estimates are currently in the 100-115 kt
range.  Based on these, the initial intensity is set at 105 kt, and
it is possible that this is a little conservative.  The hurricane
is now in a light vertical shear environment and is showing good
cirrus outflow in the southwestern semicircle.

The intensity guidance has been consistent in saying that Olivia
should weaken due to a combination of decreasing sea surface
temperatures along the forecast track and entrainment of dry air.
The hurricane has not yet followed the guidance, and the current
structure and convective trends suggest that this round of
intensification may not be finished.  After 12 h, Olivia should move
north of the 26C isotherm, and the cyclone should mostly traverse
sea-surface temperatures of 25-26C for the remainder of the forecast
period.  This development should start a weakening trend.  The new
intensity forecast allows for 12 h of additional strengthening,
followed by a gradual weakening that follows the overall trend of
the intensity guidance.  However, the new forecast lies at the upper
edge of the guidance, and thus most of the forecast intensities are
higher than those in both the previous special and regular
advisories.

Water vapor imagery shows a large deep-layer ridge to the north of
Olivia, and the large-scale models forecast the western end of the
ridge to build westward during the next several days.  This pattern
should steer the cyclone west-northwestward for the next 48 h or
so, followed by a westward motion from 72-120 h.  The track guidance
is in good agreement with this scenario, and the guidance is more
tightly clustered than it was 24 h ago.  The new forecast track is
similar to the previous track through 48 h, then it is nudged a
little to the south of the previous track from 72-120 h.  The new
track lies close to the various consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 18.4N 127.2W  105 KT 120 MPH
 12H  07/0000Z 18.9N 129.2W  110 KT 125 MPH
 24H  07/1200Z 19.8N 131.8W  100 KT 115 MPH
 36H  08/0000Z 20.5N 134.4W   90 KT 105 MPH
 48H  08/1200Z 21.2N 137.0W   80 KT  90 MPH
 72H  09/1200Z 21.5N 142.0W   70 KT  80 MPH
 96H  10/1200Z 21.5N 146.5W   65 KT  75 MPH
120H  11/1200Z 21.5N 150.5W   60 KT  70 MPH

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Forecaster Beven

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