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Tropical Storm Sergio Discussion Number   7
NWS National Hurricane Center Miami FL       EP212018
900 PM MDT Sun Sep 30 2018

Overall, Sergio has changed little in organization over the past
several hours.  The convective pattern is comprised of a ragged
band wrapping about three-quarters of the way around the center,
with the strongest convection to the north of the center.  Recent
microwave data show that the mid-level circulation center seen
earlier has lost some definition.  However, the low-level
circulation center seems to be becoming better defined.  The
initial intensity remains 55 kt based on unchanged satellite
intensity estimates.

The initial motion remains 260/11.  For the next 36 h or so, Sergio
should move westward or just south of due westward around the
southern periphery of a large deep-layer subtropical ridge extending
from Mexico westward across the eastern Pacific.  After that time, a
mid- to upper-level trough moving southeastward along and offshore
of the western U.S. will erode the western part of the ridge. This
development will allow Sergio turn west-northwestward to
northwestward with a gradual decrease in forward speed.  The new
forecast track is near the various consensus models and is an
update of the previous track.

Conditions appear favorable for Sergio to rapidly intensify in the
next 36 h if the cyclone can become well enough organized to take
advantage of the environment.  This part of the intensity forecast
presumes this will happen and is unchanged from the previous
forecast of quick strengthening.  From 36-48 h, a burst of
northeasterly shear is expected to affect Sergio, which should at
least slow intensification.  Based on this and the shear letting up
at 72 h, the intensity forecast is tweaked to show the peak
intensity after the shear decreases.  After 72 h, decreasing sea
surface temperatures along the forecast track should cause a gradual
weakening.


FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 11.6N 107.3W   55 KT  65 MPH
 12H  01/1200Z 11.4N 109.0W   65 KT  75 MPH
 24H  02/0000Z 11.3N 111.3W   80 KT  90 MPH
 36H  02/1200Z 11.6N 113.4W   95 KT 110 MPH
 48H  03/0000Z 12.4N 115.2W  100 KT 115 MPH
 72H  04/0000Z 14.5N 118.0W  105 KT 120 MPH
 96H  05/0000Z 16.5N 120.5W  100 KT 115 MPH
120H  06/0000Z 18.0N 122.5W   90 KT 105 MPH

$$
Forecaster Beven

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