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Potential Tropical Cyclone Fifteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL152017
1100 AM AST Sat Sep 16 2017

Satellite images indicate that the area of low pressure located
several hundred miles east of the Lesser Antilles has become better
organized with curved banding features now better established.
Since there is still no indication of a well-defined center and
because tropical storm watches have been issued for portions of
the Leeward Islands, NHC has initiated advisories on this system as
a potential tropical cyclone.  The initial wind speed is estimated
to be 30 kt based on a blend of the Dvorak classifications from TAFB
and SAB.

The initial motion estimate is 280/19, but this is uncertain due to
the lack of a clear center.  A slower west-northwestward motion is
expected during the next several days as a mid-level ridge to the
north of the system weakens but remains nearly stationary.  The NHC
track forecast takes the system across the Leeward Islands in a few
days and then near the Virgin Islands and Puerto Rico by the end of
the forecast period.  It should be noted that confidence in the
track and forward speed of this system is low due to the spread in
the models and the current lack of a well-defined center.

The disturbance is expected to be in environmental conditions
conducive for strengthening during the next several days as the
shear is expected to be 10 kt or less while the cyclone moves over
warm 29 deg C SSTs.  These conditions should allow for at least
steady strengthening, and the models unanimously show that trend.
The NHC intensity forecast is conservative for now, but does show
the system becoming a tropical storm later today and a hurricane by
the time it reaches the Leeward Islands.

KEY MESSAGES:

1. The disturbance is expected to intensify and will likely bring
tropical storm and hurricane conditions as well as flooding
rainfall to portions of the Lesser Antilles early next week. These
conditions could also spread into the Virgin Islands and Puerto Rico
by mid week. Interests in these areas should monitor the progress
of this system and follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 12.2N  50.5W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  17/0000Z 12.8N  52.8W   35 KT  40 MPH...TROPICAL STORM
 24H  17/1200Z 13.6N  55.1W   40 KT  45 MPH
 36H  18/0000Z 14.3N  56.9W   50 KT  60 MPH
 48H  18/1200Z 15.0N  58.6W   60 KT  70 MPH
 72H  19/1200Z 16.3N  61.3W   75 KT  85 MPH
 96H  20/1200Z 17.6N  64.0W   80 KT  90 MPH
120H  21/1200Z 18.7N  67.3W   80 KT  90 MPH

$$
Forecaster Cangialosi

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