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Hurricane Sergio Discussion Number  31
NWS National Hurricane Center Miami FL       EP212018
800 PM PDT Sat Oct 06 2018

Little overall change has been noted in Sergio's satellite
presentation the past several hours other than cloud tops have
warmed slightly. The 30-nmi-wide eye remains quite distinct and
outflow is still very impressive in all quadrants. However, he
warming tops have resulted in slightly lower satellite intensity
estimates from all agencies, so the initial intensity has been
lowered to 105 kt for this advisory.

Sergio is lumbering along toward the west, or 270/06 kt. There is no
significant change to the previous forecast track or reasoning.
Sergio should continue to move slowly westward around the
southwestern periphery of a weak deep-layer ridge for the next day
or so. By early next week, a strong trough is forecast to dig
southward off the coasts of California and Baja California, which
will erode the ridge and cause Sergio to make a sharp northeastward
turn and accelerate throughout the forecast period. The latest NHC
track guidance remains in good agreement on this developing steering
flow pattern, and there is very little cross-track spread in the
models. The speed differences noted in the previous discussion have
decreased on this forecast cycle, so only minor tweaks had to be
made to the previous advisory track. The new forecast track lies
close the previous one and near a blend of the various consensus
track models.

Ocean temperatures beneath the cyclone are forecast to decrease over
the next few days due to cold upwelling beneath the hurricane, so
gradual weakening is expected for the next 3 days. After that, more
rapid weakening is forecast due to increasing southwesterly
vertical wind shear ahead of a a deep-layer trough. The NHC
intensity forecast is very similar to the previous advisory and the
IVCN consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 14.5N 125.4W  105 KT 120 MPH
 12H  07/1200Z 14.5N 126.4W  100 KT 115 MPH
 24H  08/0000Z 14.8N 127.2W   95 KT 110 MPH
 36H  08/1200Z 15.4N 127.6W   90 KT 105 MPH
 48H  09/0000Z 16.1N 127.4W   85 KT 100 MPH
 72H  10/0000Z 18.0N 124.9W   75 KT  85 MPH
 96H  11/0000Z 20.9N 120.6W   60 KT  70 MPH
120H  12/0000Z 25.6N 115.1W   45 KT  50 MPH

$$
Forecaster Stewart

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