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Tropical Depression Twenty-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP202018
300 AM MDT Tue Sep 25 2018

The low pressure system that NHC has been monitoring off the coast
of southwestern Mexico has now become a tropical depression, the
twentieth of the eastern North Pacific 2018 season.  ASCAT data from
around 0400 UTC indicated that the system had a well-defined center
and maximum winds in the 25-30 kt range.  In addition, satellite
images show deep convection increasing in coverage and intensity
near the center.  The initial wind speed is set at 30 kt, based on
the ASCAT data, but this is a little below the latest Dvorak
estimate from TAFB.

Since the depression has only recently formed, the initial motion
is an uncertain 280/7 kt.  Mid-level ridging to the north of the
system should keep the depression on a westward to west-
northwestward path at about the same forward speed for the
next few days.  Thereafter, the models show the ridge breaking down
due to a large cut off deep-layer low moving toward the west coast
of the United States.  In response, the cyclone is expected to turn
to the northwest this weekend.  The models agree on this overall
scenario, but there is a fair amount of spread by the end of the
forecast period.  The NHC track forecast lies near the middle of
the guidance envelope and close to the best performing models, the
consensus aids.

The environmental conditions appear favorable for the depression to
strengthen.  SSTs are expected to remain quite warm beneath the
cyclone for the next several days while vertical wind shear values
are around 10 kt or less.  These conditions combined with a
moist airmass should allow for at least steady strengthening during
the next 3 to 4 days.  Some weakening is possible by the end of the
forecast period due to slightly cooler SSTs and an increase in
shear.  The NHC intensity forecast shows a slower rate of
strengthening than the guidance, since the system is still
in the developing stage, but predicts peak winds near the IVCN
consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 14.5N 107.2W   30 KT  35 MPH
 12H  25/1800Z 14.9N 108.2W   35 KT  40 MPH
 24H  26/0600Z 15.5N 109.8W   40 KT  45 MPH
 36H  26/1800Z 15.8N 111.2W   55 KT  65 MPH
 48H  27/0600Z 16.1N 112.6W   70 KT  80 MPH
 72H  28/0600Z 16.9N 115.6W   90 KT 105 MPH
 96H  29/0600Z 18.3N 118.1W   90 KT 105 MPH
120H  30/0600Z 20.7N 119.5W   85 KT 100 MPH

$$
Forecaster Cangialosi

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