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Hurricane Norman Discussion Number  15
NWS National Hurricane Center Miami FL       EP162018
200 PM PDT Fri Aug 31 2018

Satellite derived mid and upper tropospheric winds and the UW-CIMSS
shear analysis indicate that the persistent northeasterly vertical
shear has increased to 20-25 kt, and has continued to impede outer
deep convective banding development in the northern portion of
Norman's inner core.  The cloud pattern has also become somewhat
asymmetric (northeast to southwest).  A series of recent microwave
images, however, show that the eyewall is now closed, although the
eye temperature has warmed a bit during the past 6 hours.  The
Dvorak satellite intensity classifications from TAFB and SAB also
support these observations, and the initial intensity is reduced to
110 kt.

Although there may still be some fluctuations in intensity, gradual
weakening is forecast through day 5, primarily due to the shear
predicted by the GFS and ECMWF Decay-SHIPS intensity models.
Intrusion of stable air mass, beyond day 3, northeast of the
Hawaiian Islands will also promote this weakening trend.  The
official intensity forecast has changed little from the previous
advisory, and is still based on the HFIP Corrected Consensus
Approach and IVCN intensity models.

The initial motion is estimated to be west-southwest, or 255/7 kt.
An anchored mid- to upper-level ridge that stretches
west-southwestward from the Baja California peninsula should steer
Norman west-southwestward during the next 12 hours or so.
Afterward, the southwestern-most segment of the ridge axis between
Miriam and Norman weakens as Miriam continues on a northward track.
This change in the synoptic steering pattern should influence Norman
to turn back toward the west or west-northwest by early next week.
Only slight along-track speed adjustments were made to this
advisory, which follows a blend of the HCCA and TVCN consensus
guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 16.5N 121.5W  110 KT 125 MPH
 12H  01/0600Z 16.2N 122.6W  100 KT 115 MPH
 24H  01/1800Z 16.2N 124.4W   95 KT 110 MPH
 36H  02/0600Z 16.6N 127.0W   90 KT 105 MPH
 48H  02/1800Z 17.3N 129.9W   85 KT 100 MPH
 72H  03/1800Z 18.9N 136.0W   80 KT  90 MPH
 96H  04/1800Z 20.0N 141.1W   70 KT  80 MPH
120H  05/1800Z 20.9N 144.7W   65 KT  75 MPH

$$
Forecaster Roberts

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