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Tropical Depression SEVENTEEN

Tropical Depression Seventeen Discussion Number   1
NWS National Hurricane Center Miami FL       AL172021
800 AM CVT Sun Sep 19 2021
The small low pressure system that the NHC has been tracking the 
past few days has acquired a well-defined circulation and enough 
organized deep convection to be classified as a tropical depression. 
The initial intensity of 30 kt is based on 0000 UTC ASCAT wind data 
of about 30 kt. This intensity is also supported by consensus Dvorak 
satellite classifications of T2.0/30 kt from TAFB and SAB.

The initial motion estimate is north-northwestward or 330/12 kt. 
The small cyclone is forecast to move in a general northwestward 
direction throughout the remainder of the forecast period as the 
system moves along the southwestern and western periphery of a 
subtropical ridge that extends westward from Africa across the Cabo 
Verde Islands. The NHC forecast track lies down the middle of the 
tightly packed track models.

Only modest strengthening is expected during the next 48 hour so 
while the small cyclone remains over 27-28 deg C sea-surface 
temperatures and the vertical wind shear decreases to near 5 kt 
during that time. However, proximity to dry air is expected 
prevent any significant strengthening from occurring. By late 
Tuesday, a slow weakening trend is forecast to begin as the system 
moves over cooler water and the shear increases from the southwest. 
The NHC intensity forecast closely follows a blend of the IVCN and 
HCCA intensity consensus models through 72 hours, and then is lower 
than the HCCA model on days 4 and 5.
INIT  19/0900Z 11.8N  28.2W   30 KT  35 MPH
 12H  19/1800Z 13.4N  29.2W   35 KT  40 MPH
 24H  20/0600Z 15.5N  31.2W   40 KT  45 MPH
 36H  20/1800Z 17.6N  33.2W   40 KT  45 MPH
 48H  21/0600Z 19.7N  34.7W   35 KT  40 MPH
 60H  21/1800Z 21.7N  36.1W   35 KT  40 MPH
 72H  22/0600Z 23.2N  37.2W   30 KT  35 MPH
 96H  23/0600Z 25.6N  39.6W   30 KT  35 MPH
120H  24/0600Z 28.1N  41.5W   30 KT  35 MPH
Forecaster Stewart