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Tropical Depression Fifteen-E Discussion Number   4
NWS National Hurricane Center Miami FL       EP152017
800 AM PDT Tue Sep 12 2017

The first-light visible imagery from the GOES-16 satellite depicts
a tightly wound low-level center with all of the deep convection
west of the center.  The initial intensity is set to 30 kt - just a
bit higher than previously, based upon the TAFB Dvorak
classification.

The dislocation of the deep convection is symptomatic of the
moderate to strong vertical shear, forced by the upper-level ridge
to the north of the depression.  Moderate shear should continue for
the next couple of days, limiting the opportunity for the system to
intensify.  In about two days, the depression may begin interacting
with a developing tropical cyclone to its east.  One plausible
scenario is for the system to be absorbed by the new tropical
cyclone.  The official forecast instead shows a gradual weakening
as the depression tracks slowly westward, due to an increasingly
hostile upper-level environment.  The intensity forecast is a
little above the previous one in respect to the slightly improved
structure shown this morning and is closest to the HFIP Corrected
Consensus Approach.

The depression is moving toward the west at 13 kt, primarily being
steered by the deep-layer ridge to its north.  The depression
should continue moving in this general direction at a slower rate
of forward speed during the next couple of days.  At days three and
four, the low-level steering flow should weaken due to the
developing tropical cyclone to the depression's east.  The official
track forecast is based upon the model consensus minus the UKMET
(whose tracker latches on to the developing tropical cyclone
instead) and is east of that from the previous advisory.  This track
prediction has higher uncertainty than usual because of the
divergence of plausible outcomes for the depression.


FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 15.6N 116.2W   30 KT  35 MPH
 12H  13/0000Z 15.2N 117.7W   35 KT  40 MPH
 24H  13/1200Z 14.9N 119.2W   35 KT  40 MPH
 36H  14/0000Z 14.9N 120.5W   30 KT  35 MPH
 48H  14/1200Z 15.1N 121.5W   30 KT  35 MPH
 72H  15/1200Z 15.6N 122.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  16/1200Z 15.7N 123.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  17/1200Z...DISSIPATED

$$
Forecaster Landsea

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