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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.
FORECAST POSITIONS AND MAX WINDS
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