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Tropical Depression TWENTY-TWO-E


Tropical Depression Twenty-Two-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP222018
1000 AM CDT Sun Oct 14 2018

A small low pressure system that the NHC has been tracking for the
past couple of days has finally acquired enough organized convection
to be designated a tropical depression, which is located less than
100 nmi off the southwestern coast of Mexico. Cloud tops near the
center have recently been as cold as -90C, and satellite intensity
estimates are T1.5/25 kt from both TAFB and SAB. The initial
intensity is set at 30 kt based on an earlier OSCAT/ScatSat
scatterometer pass that had a few uncontaminated wind vectors
located just north of a well-defined low-level circulation center,
which is similar to yesterday's ASCAT passes.

The initial motion estimate is 295/05 kt. The small cyclone is
forecast by the global and regional models to move only slowly
westward to southwestward at less than 5 kt for the new few days due
to the system being caught in a break in the subtropical ridge that
extends from central Mexico southwestward into the eastern Pacific.
By days 4 and 5, the ridge is forecast to build westward to the
north of the system, acting to nudge the cyclone westward at a
slightly faster forward speed. The NHC forecast track lies between
the consensus models TVCE and HCCA.

The environment is expected to be somewhat conducive for gradual
strengthening of the cyclone throughout the forecast period. The
statistical-dynamical models SHIPS and LGEM aren't overly enthused
with intensifying the system, but that is mainly due to the high
shear values calculated from the very poleward TABM beta-advection
model, which recurves the cyclone into strong mid-latitude flow on
days 4 and 5. In contrast, the HWRF model keeps the system farther
south and gradually develops the cyclone into a hurricane by 72 h,
and then continues with slight strengthening beyond that time. Given
that the shear is expected to only be around 10 kt from an easterly
to southeasterly direction and water temperatures near 30 deg C
beneath the small cyclone, some gradual strengthening appears to be
plausible with only some slight land interaction being the primary
modulating factor until the system moves farther away from Mexico in
about 72 h.

Based on the small size of the circulation and its projected motion
away from Mexico, tropical storm warnings and watches are not
required at this time. However, only a slight deviation to the right
of the forecast track would bring stronger winds closer to the
coast, which would require the issuance of a tropical storm warning.
Regardless, heavy rainfall will be the primary threat along the
coast of southwestern Mexico due to the system's slow motion, and
flash flooding will be a possibility in mountainous areas.


INIT  14/1500Z 17.0N 102.8W   30 KT  35 MPH
 12H  15/0000Z 17.2N 103.6W   35 KT  40 MPH
 24H  15/1200Z 17.2N 103.8W   35 KT  40 MPH
 36H  16/0000Z 17.0N 103.8W   40 KT  45 MPH
 48H  16/1200Z 16.6N 103.6W   45 KT  50 MPH
 72H  17/1200Z 16.3N 104.4W   60 KT  70 MPH
 96H  18/1200Z 16.5N 105.9W   70 KT  80 MPH
120H  19/1200Z 16.9N 107.5W   80 KT  90 MPH

Forecaster Stewart