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Hurricane Sergio Discussion Number  37
NWS National Hurricane Center Miami FL       EP212018
800 AM PDT Mon Oct 08 2018

Sergio's structure has remained nearly steady-state for the past 24
hours.  A solid ring of deep convection surrounds Sergio's giant
eye, and there is little evidence of any convective bands.  Despite
upwelling that is presumably occuring beneath the slow moving
hurricane, cloud tops have actually cooled over the past few hours,
and satellite intensity estimates from TAFB and SAB have not
changed. The initial intensity has therefore been held at 80 kt,
which also agrees with a 1045 UTC UW-CIMSS SATCON estimate.

As long as Sergio can maintain its annular structure in an
environment of negligible shear, only very gradual weakening is
expected, despite presumably cooling waters beneath the cyclone
associated with its slow movement.  The ECMWF and GFS forecast that
the shear will begin to increase in about 24 to 36 hours, and the
cyclone will also be reaching much cooler waters shortly after that
time.  A faster rate of weakening is therefore anticipated beyond
48 h, in line with the latest intensity consensus, and Sergio is
forecast to be a tropical storm when it approaches northwestern
Mexico in a few days.  The cyclone should weaken quickly after
landfall, and will likely dissipate over the high terrain of
mainland Mexico, though a 5 day remnant low point is still shown
for continuity purposes.

Sergio is moving very little right now, and the slow motion will
likely continue during the day today.  By tonight, a large trough
centered over the southwestern United States will cause the
hurricane to accelerate northeastward.  The track guidance is in
good agreement on the track of Sergio, although there is still some
uncertainty associated with the timing for when Sergio will reach
the west coast of the Baja California peninsula. Only minor changes
were made to the official track forecast, which lies near the middle
of the guidance envelope and very close to TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 15.3N 128.6W   80 KT  90 MPH
 12H  09/0000Z 15.9N 128.4W   75 KT  85 MPH
 24H  09/1200Z 16.6N 127.6W   70 KT  80 MPH
 36H  10/0000Z 17.4N 126.1W   65 KT  75 MPH
 48H  10/1200Z 18.6N 124.0W   65 KT  75 MPH
 72H  11/1200Z 22.3N 119.0W   55 KT  65 MPH
 96H  12/1200Z 27.5N 113.0W   40 KT  45 MPH...INLAND
120H  13/1200Z 33.0N 105.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky

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