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Tropical Depression FOUR


Tropical Depression Four Discussion Number   2
NWS National Hurricane Center Miami FL       AL042017
500 AM AST Thu Jul 06 2017

The cloud pattern of the tropical cyclone consists mainly of a
circularly shaped mass of deep convection that has persisted
overnight.  Since there has been little overall change in the
satellite appearance of the system, the current intensity estimate
remains 25 kt, which is also in agreement with a Dvorak estimate
from SAB.

Dry and dusty air related to the Saharan Air Layer, to the east of
the tropical cyclone, is beginning to wrap around the northern part
of the depression's circulation.  Dynamical models indicate that
this air mass will be partially entrained into the system over the
next couple of days.  This, combined with increasing vertical
shear, should prevent significant strengthening of the system.
Although the statistical-dynamical guidance, SHIPS and LGEM,
forecast some modest intensification of the tropical cyclone, these
models have been known to have a high bias at times.  The GFS,
UKMET, and ECMWF global models all show the system quickly
degenerating to a wave.  As a compromise between the global and the
statistical-dynamical guidance, the official forecast more or less
maintains the cyclone's intensity for a couple of days followed by
weakening to a remnant low in 72 hours and dissipation after 96

The center is not very easy to locate, but based on continuity with
earlier data it is believed to be near the eastern edge of the
convective mass.  There has apparently been some acceleration and
the motion is now estimated to be 290/15 kt.  The flow on the
southern side of a subtropical ridge should continue to steer the
tropical cyclone, or its remnants, west-northwestward over the next
few days.  The official track forecast follows a trajectory very
similar to the previous one, but is somewhat faster.  This is close
to the latest model consensus.


INIT  06/0900Z 13.2N  40.0W   25 KT  30 MPH
 12H  06/1800Z 14.0N  42.5W   30 KT  35 MPH
 24H  07/0600Z 15.0N  46.2W   30 KT  35 MPH
 36H  07/1800Z 16.3N  50.0W   30 KT  35 MPH
 48H  08/0600Z 17.5N  53.5W   25 KT  30 MPH
 72H  09/0600Z 20.5N  59.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  10/0600Z 23.0N  65.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  11/0600Z...DISSIPATED

Forecaster Pasch