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Tropical Storm SERGIO


ZCZC MIATCDEP1 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Sergio Discussion Number   2
NWS National Hurricane Center Miami FL       EP212018
400 PM CDT Sat Sep 29 2018

Recent scatterometer data confirms that Sergio is at tropical storm
strength, but with a slightly unexpected twist - the maximum winds
are in a band about 110 n mi east of the center and there is no
inner wind core at this time.  The initial intensity remains 35 kt
based on the scatterometer data.  Sergio currently has good cirrus
outflow in all directions, but there is some evidence that northerly
upper-level winds below the level of the outflow are causing some
light shear.

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.
The environment is favorable enough for rapid intensification,
although the current storm structure does not appear favorable for
quick strengthening.  The intensity forecast calls for gradual
intensification during the first 24-36 h, with a faster rate from
36-72 h as the cyclone becomes better organized.  Near the end of
the forecast period, the storm may encounter increasing
northeasterly shear which could limit intensification, and this is
reflected in the forecast.  The intensity forecast is in the middle
of the guidance envelope and just above the intensity consensus,
and the forecast may need to be adjusted upward in subsequent
advisories.  The wind radii forecast have been adjusted based on
the current structure and the latest radii guidance.

The initial motion is now 275/10.  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 remains in good agreement with this
scenario, and the new forecast track is similar to, but a little
south of, the previous track.


FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 12.1N 102.8W   35 KT  40 MPH
 12H  30/0600Z 12.3N 104.3W   40 KT  45 MPH
 24H  30/1800Z 12.3N 106.3W   50 KT  60 MPH
 36H  01/0600Z 12.2N 108.3W   60 KT  70 MPH
 48H  01/1800Z 12.1N 110.2W   75 KT  85 MPH
 72H  02/1800Z 13.0N 114.0W   95 KT 110 MPH
 96H  03/1800Z 15.0N 117.5W   95 KT 110 MPH
120H  04/1800Z 16.5N 119.5W   95 KT 110 MPH

$$
Forecaster Beven

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