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Hurricane OLIVIA


Hurricane Olivia Discussion Number  25
NWS National Hurricane Center Miami FL       EP172018
200 PM PDT Thu Sep 06 2018

Olivia has continued to strengthen since the previous advisory,
with the eye becoming better defined inside of the central dense
overcast.  The various satellite intensity estimates range from
100-120 kt, and the initial intensity is nudged upward to 110 kt in
agreement with the CIMSS satellite consensus.  The hurricane
remains in a light vertical shear environment and is showing good
cirrus outflow, especially in the southwestern semicircle.

Olivia should remain in a light shear environment during the
forecast period, so sea surface temperatures and environmental
moisture should be the main controls on the intensity.  The
hurricane should reach the 26C sea surface temperature isotherm in
about 12 h, and this should finally cause the hurricane to weaken.
The forecast track keeps the cyclone over 25-26C sea surface
temperatures through about the 72 h point as it also encounters a
drier airmass, and thus the intensity forecast shows weakening
consistent with the trend of the intensity guidance.  After 72 h,
the waters along the forecast track begin to warm, but the airmass
near Olivia gets even drier.  The guidance shows continued weakening
during this time, so the intensity forecast follows suit. However,
there is lower confidence in this portion of the forecast.

Water vapor imagery continues to show 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
tightly clustered track guidance supports this scenario, and the
new forecast track is changed little from the previous forecast.


INIT  06/2100Z 18.6N 128.5W  110 KT 125 MPH
 12H  07/0600Z 19.2N 130.5W  110 KT 125 MPH
 24H  07/1800Z 20.0N 133.0W  100 KT 115 MPH
 36H  08/0600Z 20.7N 135.6W   90 KT 105 MPH
 48H  08/1800Z 21.2N 138.2W   80 KT  90 MPH
 72H  09/1800Z 21.5N 143.5W   70 KT  80 MPH
 96H  10/1800Z 21.5N 147.5W   65 KT  75 MPH
120H  11/1800Z 21.5N 151.5W   60 KT  70 MPH

Forecaster Beven