Official Discussion issued by the National Hurricane Center

Seventeen (AL172017) DATA RELEASED: 10/9/2017 5:00:00 AM UTC

Copy of official data

Tropical Depression Seventeen Discussion Number   1
NWS National Hurricane Center Miami FL       AL172017
500 AM AST Mon Oct 09 2017

The well-defined low pressure system over the eastern Atlantic
several hundred miles southwest of the Azores has maintained an
area of deep convection near and to the east of the center for the
past several hours.  Therefore, the system now meets the criteria
for a tropical depression.  The initial intensity is estimated to be
30 kt based on ASCAT data from around 0000 UTC and a 2.0/30 kt
Dvorak classification from TAFB.

The depression is moving slowly northward at 3 kt, and a continued
slow north to north-northeast motion is expected today.  A turn to
the east and then southeast is forecast to begin tonight and
continue through Wednesday while the cyclone is steered by the flow
on the east side of a subtropical ridge.  Thereafter, a mid- to
upper-level trough is expected to approach the depression, and that
should cause the system to move a little faster to the east and
east-northeast.  The NHC track forecast lies near the middle of the
guidance envelope, in agreement with various consensus aids, and
keeps the system far from any land areas.

The depression is currently over marginally warm 27 deg C SSTs and
in an environment of moderate to strong westerly shear.   The
models suggest that the shear will likely let up a little during the
next couple of days, which could allow the depression to gradually
strengthen while it remains over relatively warm waters.  After that
time, the shear could increase again, but the amount of shear
depends on the exact track of the tropical cyclone.  There is a fair
amount of spread in the models at the longer range with the regional
models (HWRF, HMON, and COAMPS-TC) bringing the system to hurricane
strength while the statistical SHIPS and LGEM models show a much
weaker system.  The NHC intensity forecast leans toward the more
conservative side of the guidance for now, but it should be noted
that confidence in the intensity forecast is low.


INIT  09/0900Z 31.1N  39.9W   30 KT  35 MPH
12H  09/1800Z 31.5N  39.8W   35 KT  40 MPH
24H  10/0600Z 31.7N  39.0W   35 KT  40 MPH
36H  10/1800Z 31.5N  38.4W   40 KT  45 MPH
48H  11/0600Z 31.0N  37.8W   45 KT  50 MPH
72H  12/0600Z 29.7N  37.0W   50 KT  60 MPH
96H  13/0600Z 29.7N  35.5W   50 KT  60 MPH
120H  14/0600Z 31.0N  32.0W   50 KT  60 MPH

Forecaster Cangialosi