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Tropical Storm SERGIO


Tropical Storm Sergio Discussion Number  10
NWS National Hurricane Center Miami FL       EP212018
300 PM MDT Mon Oct 01 2018

Sergio has not strengthened like the models and NHC have predicted
up to this point.  Although the storm continues to have a
well-defined curved band over the south and east portions of the
circulation, there are pronounced dry slots that have entrained into
the inner core.  Recent microwave images show a well-defined
low-level eye, but the mid-level structure is less organized now as
compared to several hours ago.  The initial intensity is again held
at 60 kt, in agreement with an average of the Dvorak classifications
from TAFB and SAB.

The intensity forecast remains challenging.  The wind shear around
Sergio is expected to be low for the next several days, besides for
a brief increase in the 24- to 48-hour time period.  These
conditions and warm SSTs beneath the cyclone during the next few
days support strengthening.  However, as mentioned above, the storm
has been struggling with dry air entrainment and that could continue
to plague the system.  The latest models continue to show steady
strengthening, and the NHC forecast does likewise.  However, this
forecast shows a slower rate of intensification in the short term.
Beyond a few days, a combination of slightly lower SSTs and a
decrease in moisture should cause a slow weakening trend.  The NHC
intensity forecast is in best agreement with the IVCN model.

Sergio is moving just south of due west at 11 kt.  A westward
motion at about the same forward speed is expected during the next
day or so while the storm remains on the south side of a mid-level
ridge.  A turn to the west-northwest is expected by late Tuesday
followed by a northwestward motion on Wednesday as the western
portion of the mid-level ridge erodes due to a large scale mid- to
upper-level trough near the southwestern U.S. 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
have shifted to the south and west this cycle, and the NHC track
forecast has been adjusted in those directions.


INIT  01/2100Z 11.3N 111.0W   60 KT  70 MPH
 12H  02/0600Z 11.3N 112.7W   70 KT  80 MPH
 24H  02/1800Z 11.6N 114.8W   80 KT  90 MPH
 36H  03/0600Z 12.4N 116.5W   90 KT 105 MPH
 48H  03/1800Z 13.5N 118.0W   95 KT 110 MPH
 72H  04/1800Z 15.4N 120.2W  100 KT 115 MPH
 96H  05/1800Z 17.0N 123.0W   95 KT 110 MPH
120H  06/1800Z 17.8N 126.0W   85 KT 100 MPH

Forecaster Cangialosi