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Tropical Storm Sergio Discussion Number   9
NWS National Hurricane Center Miami FL       EP212018
900 AM MDT Mon Oct 01 2018

Sergio is almost a hurricane.  Satellite images indicate that the
central convection has been increasing in intensity during the past
several hours, but there are still no indications of an eye in
that data.  Microwave imagery does show an eye feature, however.
The outer bands are not particularly well organized, and there are
some dry slots beyond the inner core.  The initial intensity is held
at 60 kt, following a blend of the latest Dvorak estimates.

As mentioned in the previous discussion, the models have been too
bullish on Sergio strengthening during the past couple of days.
This could be due to the aforementioned dry slots that were not well
predicted by both the statistical and dynamical guidance.  Looking
ahead to the next several days, the environmental conditions are
mixed.  The wind shear and SSTs appear conducive for strengthening
during the next couple of days, so steady intensification is
predicted during that time period.  However, as seen during the past
day or two, dry air could slow the intensification rate.  Beyond a
couple of days, the models show a brief increase in shear and a
steady decrease in mid-level moisture and SSTs.  These conditions
will likely end the opportunity for strengthening and cause a slow
weakening trend.  The NHC intensity forecast is about the same as
the previous one, and it lies between the usually reliable HCCA and
IVCN consensus models.

Sergio is moving westward at 10 kt steered by a mid-level ridge to
its north and northeast.  A continued westward motion is expected
for another day followed by a turn to the west-northwest and then
the northwest as the western side of the ridge weakens due to a
large-scale trough near the southwestern United States.  By the end
of the forecast period, a ridge is expected to build to the north of
Sergio, which should cause a turn back to the left.  The models are
in very good agreement overall, and little change has been made to
the previous forecast track.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 11.5N 109.5W   60 KT  70 MPH
 12H  02/0000Z 11.4N 111.2W   70 KT  80 MPH
 24H  02/1200Z 11.7N 113.4W   85 KT 100 MPH
 36H  03/0000Z 12.4N 115.3W   95 KT 110 MPH
 48H  03/1200Z 13.3N 116.8W  100 KT 115 MPH
 72H  04/1200Z 15.3N 119.3W  100 KT 115 MPH
 96H  05/1200Z 17.0N 121.8W   95 KT 110 MPH
120H  06/1200Z 18.0N 124.3W   85 KT 100 MPH

$$
Forecaster Cangialosi

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