354 
WTPZ41 KNHC 291535
TCDEP1

Tropical Storm Sergio Special Discussion Number   1
NWS National Hurricane Center Miami FL       EP212018
1030 AM CDT Sat Sep 29 2018

Satellite imagery indicates that convection associated with the low
pressure area south-southwest of Acapulco has continued to become
better organized, with the low-level center embedded under the
convective overcast and near a developing complex of bands in the
southeastern semicircle.  Based on this and continuity from earlier
scatterometer data, advisories are being initiated on Tropical
Storm Sergio with 35 kt winds.

Sergio is expected to be in an environment of light vertical shear
and high humidity, and over warm sea surface temperatures for the
next 3 days or so, which should result in steady strengthening. Near
the end of the forecast period, the storm may encounter increasing
northeasterly shear which could limit intensification. The intensity
forecast, which is near the intensity consensus, calls for steady
strengthening through 96 h, with Sergio becoming a hurricane by 48
h.

The initial motion is a somewhat uncertain 285/11.  Sergio should
be steered generally westward for the next three days or so by the
subtropical ridge over Mexico.  After that time, the cyclone should
approach a weakness in the ridge caused by a large mid- to
upper-level trough over California, and this should lead to a turn
toward the northwest.  The track guidance is in good agreement
with this scenario, and the forecast track lies near the HCCA
corrected consensus model.


FORECAST POSITIONS AND MAX WINDS

INIT  29/1530Z 12.4N 102.1W   35 KT  40 MPH
 12H  30/0000Z 12.7N 103.5W   35 KT  40 MPH
 24H  30/1200Z 12.9N 105.3W   40 KT  45 MPH
 36H  01/0000Z 12.9N 107.3W   50 KT  60 MPH
 48H  01/1200Z 12.8N 109.3W   65 KT  75 MPH
 72H  02/1200Z 13.0N 113.5W   85 KT 100 MPH
 96H  03/1200Z 15.0N 117.0W   95 KT 110 MPH
120H  04/1200Z 16.5N 119.0W   95 KT 110 MPH

$$
Forecaster Beven