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Tropical Depression Twelve Discussion Number   1
NWS National Hurricane Center Miami FL       AL122021
800 PM CVT Tue Aug 31 2021

Satellite imagery, along with earlier scatterometer data, indicates 
that the low pressure area over the eastern tropical Atlantic has 
a well-defined circulation and sufficient organized convection to 
be considered a tropical depression.  Thus, advisories are being 
initiated on Tropical Depression Twelve.  The initial intensity is 
set at 30 kt based on satellite intensity estimates from TAFB and 
SAB as well as the scatterometer data.

The initial motion is a somewhat uncertain 285/14.  A strong low- 
to mid-level ridge to the north should cause the cyclone to move 
westward at a faster forward speed for the next 36 h or so, 
followed by a gradual turn toward the west-northwest and northwest 
by the end of the period as the depression moves along the 
southwest side of the ridge.  There is some spread in the guidance 
after 36-48 h, with the GFS and GFS ensemble mean showing a more 
northward motion while the UKMET and the UKMET ensemble mean show a 
more westward motion.  The official forecast is near the middle of 
the guidance envelope and is close to the HFIP corrected consensus 
model, which is a little to the south of the other consensus models.

Conditions appear favorable for intensification during the next 72 
h or so as the cyclone is in a moist environment with light shear 
and warm sea surface temperatures.  The intensity forecast thus 
calls for the cyclone to become a tropical storm in 12 h or so and 
reach hurricane strength in 48-60 h.  By the end of the forecast 
period, the forecast track takes the cyclone over slightly cooler 
water and into a drier air mass.  Based on this, the intensity 
forecast calls for a slower development rate.  The official 
intensity forecast is in the middle of the intensity guidance, and 
it is possibly conservative given that many of the global models 
are showing the development of a large and powerful tropical 
cyclone.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/2100Z 11.2N  21.1W   30 KT  35 MPH
 12H  01/0600Z 11.6N  23.9W   35 KT  40 MPH
 24H  01/1800Z 12.0N  27.5W   40 KT  45 MPH
 36H  02/0600Z 12.1N  30.7W   50 KT  60 MPH
 48H  02/1800Z 12.5N  33.7W   60 KT  70 MPH
 60H  03/0600Z 13.3N  36.5W   70 KT  80 MPH
 72H  03/1800Z 14.3N  39.0W   80 KT  90 MPH
 96H  04/1800Z 16.5N  43.5W   85 KT 100 MPH
120H  05/1800Z 19.5N  47.5W   90 KT 105 MPH
 
$$
Forecaster Beven
 
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