Tropical Depression Eighteen Discussion Number   2
NWS National Hurricane Center Miami FL       AL182020
200 PM CVT Mon Sep 07 2020

Tropical Depression Eighteen is very near tropical storm strength. 
Satellite images show banding features gradually organizing on the 
west side of the circulation.  An ASCAT-B overpass showed maximum 
winds around or slightly above 30 kt in the bands to the northwest 
of the center. The Dvorak classifications from TAFB and SAB are 
lower, however.  The initial intensity is held at 30 kt for now, 
but it seems very likely that the depression will become a tropical 
storm later today.

The cyclone is moving west-northwestward at 9 kt.  A subtropical 
ridge situated to the north of the system is expected to build 
westward across the eastern Atlantic during the next 3 or 4 days.  
This steering pattern should keep the system on a general 
west-northwestward course during that time.  By the weekend, the 
depression will likely be moving into a weakness in the ridge, 
which should cause a turn to the northwest.  The models are in good 
agreement during the next few days, but there is increasing spread 
in the guidance by the end of the forecast period.  The NHC 
forecast is very similar to the previous one and lies near the 
various consensus models.

The depression will likely strengthen during the next few days as 
it remains in conducive environmental conditions of low wind shear, 
relatively warm waters, and a moist airmass.  There will likely be 
an increase in shear by the end of the week and this weekend, which 
should end the strengthening trend and perhaps induce some 
weakening at that time.  The NHC intensity forecast is largely an 
update of the previous one, and lies near the high end of the model 
guidance.

Key Messages:

1. The depression is forecast to strengthen into a tropical storm 
later today and tropical storm conditions are expected to spread 
over portions of the Cabo Verde Islands later today and tonight.  A 
Tropical Storm Warning is in effect for those islands.

2. The depression is expected to bring locally heavy rainfall to 
portions of the Cabo Verde Islands through Tuesday morning.

FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 15.7N  21.2W   30 KT  35 MPH
12H  08/0000Z 16.1N  23.1W   35 KT  40 MPH
24H  08/1200Z 16.5N  25.8W   45 KT  50 MPH
36H  09/0000Z 16.9N  28.6W   50 KT  60 MPH
48H  09/1200Z 17.4N  31.5W   55 KT  65 MPH
60H  10/0000Z 18.0N  34.1W   60 KT  70 MPH
72H  10/1200Z 18.6N  36.5W   65 KT  75 MPH
96H  11/1200Z 20.6N  40.6W   70 KT  80 MPH
120H  12/1200Z 23.2N  43.8W   65 KT  75 MPH

$$
Forecaster Cangialosi