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Tropical Depression Seventeen Forecast Discussion


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000
WTNT42 KNHC 191454
TCDAT2

Tropical Depression Seventeen Discussion Number   2
NWS National Hurricane Center Miami FL       AL172021
200 PM CVT Sun Sep 19 2021

The low-level center of the depression was exposed on visible 
satellite imagery this morning but recently a new burst has formed. 
Since the morning scatterometer passes missed the depression, the 
intensity is held at 30 kt based on consensus T-2.0 values from TAFB 
and SAB. 

The initial motion estimate is 330/12.  The 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.  No significant changes 
were made to the previous NHC forecast track, and the new 
prediction lies near the middle of the tightly clustered track 
models.

Environmental conditions are conducive for strengthening during the 
next day or so, with wind shear forecast to drop off later today.  
Thus, the official forecast calls for strengthening during the next 
24 hours, and is close to the lower half of the intensity guidance 
envelope, near the weaker global models.  This forecast could be 
conservative, since SSTs will be near 27C and mid-level atmospheric 
moisture will be enough to support intensification.  By 36-48 hours, 
the southwesterly shear will increase, which should end the 
opportunity for strengthening, and will likely cause slow weakening. 
The models hold onto this system through the 5 day period, but it is 
possible that the cyclone could become a remnant low in 4-5 days if 
the shear is too much for the system to handle.


FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 13.2N  28.8W   30 KT  35 MPH
 12H  20/0000Z 14.7N  30.1W   35 KT  40 MPH
 24H  20/1200Z 16.7N  32.2W   40 KT  45 MPH
 36H  21/0000Z 18.9N  33.9W   40 KT  45 MPH
 48H  21/1200Z 21.0N  35.4W   35 KT  40 MPH
 60H  22/0000Z 22.7N  36.5W   35 KT  40 MPH
 72H  22/1200Z 24.0N  37.6W   35 KT  40 MPH
 96H  23/1200Z 26.3N  39.9W   30 KT  35 MPH
120H  24/1200Z 28.3N  41.2W   30 KT  35 MPH

$$
Forecaster Hagen/Blake