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Tropical Depression FIFTEEN-E


Tropical Depression Fifteen-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP152017
300 PM MDT Mon Sep 11 2017

The remnants of Atlantic Hurricane Katia have redeveloped after
reaching the Pacific Ocean a couple of days ago.  The system
maintained a mid-level circulation while transiting the high terrain
of Mexico, but had lost its surface center.  Yesterday, deep
convection began in association with the mid-level circulation and
today a well-defined surface center formed.  While it was originally
thought that the convection would be sporadic because of the
moderate vertical shear, the deep convection has instead persisted
close to the system's center during the last several hours.  Since
the system now meets the definition of a tropical cyclone,
advisories are initiated as Tropical Depression Fifteen.

The depression is moving toward the west at 13 kt, steered
primarily by the deep-layer ridge to its north.  The official track
forecast is a westward or west-southwestward motion at a slower
rate of forward speed during the next two days, then a turn back
toward the west or west-northwest at days 3 and 4.  This forecast
is based upon a blend of the GFS and ECMWF global models, as the
remaining guidance either doesn't know about the depression or
unrealistically intensifies it and takes it toward the north.

The system likely will not become very substantial.  The moderate
shear should continue, while the depression heads toward cool SSTs
and dry air.  The official intensity forecast shows just modest
strengthening to a low-end tropical storm in about a day, before
weakening begins.  Deep convection may cease in about three days,
marking the system's transition to a remnant low.  The intensity
forecast is based upon the LGEM/DSHIP statistical guidance as the
mesoscale dynamical models spin the depression up to near hurricane
strength, which is not plausible.  If the system does reach
tropical storm intensity - by no means assured, then it
would be named "Max", not "Katia".


INIT  11/2100Z 16.4N 112.3W   25 KT  30 MPH
 12H  12/0600Z 16.2N 114.1W   30 KT  35 MPH
 24H  12/1800Z 15.8N 116.2W   35 KT  40 MPH
 36H  13/0600Z 15.4N 118.0W   30 KT  35 MPH
 48H  13/1800Z 15.3N 119.6W   25 KT  30 MPH
 72H  14/1800Z 15.7N 121.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  15/1800Z 16.0N 123.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  16/1800Z...DISSIPATED

Forecaster Landsea