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Hurricane Sergio Discussion Number  21
NWS National Hurricane Center Miami FL       EP212018
800 AM PDT Thu Oct 04 2018

Sergio remains a strong hurricane this morning, with subjective
Dvorak estimates range from 5.5 (102 kt) to 6.5 (127 kt).  While
some slightly drier air has been ingested into the eyewall, cloud
top temperatures have cooled recently and Sergio appears poised to
once again close off this dry air channel.  Based on these data, the
initial intensity is held at 120 kt.  The intensity forecast is
mostly a continuation of the previous advisory, but is slightly
lower after 24 hours to reflect a blend of HCCA and other consensus
aids. Vertical wind shear from GFS/SHIPS is forecast to remain at or
below approximately 10 kt through 48 hours before increasing to
above 15 kt by Saturday. The primary limiter on Sergio's intensity
appears to be SSTs which will drop off gradually, especially by the
end of the forecast.

Sergio is continuing to move northwestward around the mid-level
ridge which extends into the Pacific off of Mexico.  The initial
motion is 320/8 kt.  Objective track guidance is in fairly good
agreement on a gradual turn toward the west tonight and Friday in
response to a second ridge which builds in from the west.  Guidance
remains in decent agreement on Sergio then turning back
northeastward by the end of the forecast period as this ridge lifts
northward and a highly-amplified mid-level trough digs into western
North America.  The official track forecast is very similar to the
previous advisory through day 4 with a small shift eastward
thereafter to reflect a slightly earlier northeast turn in the
guidance.  This track philosophy is supported by essentially all of
the ECMWF/GFS ensemble members as well.

FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 15.0N 119.3W  120 KT 140 MPH
 12H  05/0000Z 15.6N 120.2W  120 KT 140 MPH
 24H  05/1200Z 16.0N 121.5W  110 KT 125 MPH
 36H  06/0000Z 16.0N 122.8W  100 KT 115 MPH
 48H  06/1200Z 15.7N 124.1W   90 KT 105 MPH
 72H  07/1200Z 15.6N 126.6W   85 KT 100 MPH
 96H  08/1200Z 16.3N 128.2W   80 KT  90 MPH
120H  09/1200Z 17.9N 127.6W   70 KT  80 MPH

$$
Forecaster Onderlinde/Cangialosi

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