Official Discussion issued by the National Hurricane Center

Seventeen (AL172020) DATA RELEASED: 9/7/2020 9:00:00 AM UTC

Copy of official data

Tropical Depression Seventeen Discussion Number   2
NWS National Hurricane Center Miami FL       AL172020
500 AM AST Mon Sep 07 2020

Tropical Depression Seventeen is a large tropical cyclone, with its
circulation evident several hundred miles from its center. An area
of deep convection has developed tonight just over and to the east
of its center with cloud top temperatures as low as -80 degrees C.
However, there appears to be some dry air in the northwestern
portion of the cyclone's circulation limiting convection there. The
latest Dvorak satellite intensity estimates from TAFB and UW-CIMSS
support keeping the initial intensity at 30 kt.

The depression has been moving west-northwestward at about 5 kt
over the past 12 hours. This general motion is expected to continue 
throughout the 5-day forecast period, with some increase in 
forward speed over the next couple of days as the cyclone is 
steered by a weak mid-level ridge to its north. The overall 
guidance shifted slightly to the north through day 3 and the latest 
NHC forecast lies in between the previous one and the consensus 
track guidance through this time period. For days 3 through 5, the 
forecast track is little changed from the previous one and is in 
good agreement with the fairly tightly clustered track guidance. 

Other than some dry air in the vicinity of the depression, the 
overall environment looks favorable for strengthening over the next 
few days. However, due to the large size of the circulation, 
strengthening may occur more slowly than what might be expected from 
a more compact cyclone. Therefore, only gradual strengthening is 
indicated in the official forecast during that time. By 72 h, 
increasing vertical wind shear should limit further intensification, 
and may cause some weakening to occur. The latest NHC intensity 
forecast is a blend of the previous one and the HFIP corrected 
consensus, HCCA.


INIT  07/0900Z 17.3N  42.1W   30 KT  35 MPH
12H  07/1800Z 17.5N  42.6W   35 KT  40 MPH
24H  08/0600Z 17.8N  43.2W   35 KT  40 MPH
36H  08/1800Z 18.3N  44.1W   40 KT  45 MPH
48H  09/0600Z 19.1N  45.6W   45 KT  50 MPH
60H  09/1800Z 19.7N  47.1W   50 KT  60 MPH
72H  10/0600Z 20.1N  49.0W   50 KT  60 MPH
96H  11/0600Z 20.6N  52.7W   45 KT  50 MPH
120H  12/0600Z 21.7N  55.5W   45 KT  50 MPH

Forecaster Latto