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Tropical Depression Ten Discussion Number   1
NWS National Hurricane Center Miami FL       AL102021
500 AM AST Sat Aug 28 2021

The tropical wave and associated low pressure system that the NHC 
has been tracking for the past several days has finally acquired a 
well-defined surface circulation and enough organized deep 
convection to be classified as a tropical depression. The last few 
visible satellite images yesterday evening indicated a tight swirl 
in the low-cloud field and a 27/2325Z partial ASCAT-A pass showed 
the circulation was also well-defined, albeit with only 23-kt 
surface winds. Since the time of that scatterometer pass, however, a 
significant increase in deep convection with cloud tops colder than 
-80 deg C has developed very near and to the northeast of he center, 
with a few cells also now having developed just to the southwest of 
the center. Based on the structure noted in the ASCAT data and the 
pronounced increase in the amount and organization of the 
convection, the advisory intensity is estimated to be 30 kt.

The initial motion estimate is 340/06 kt. The system has slowed down 
markedly during the past several hours, likely due to the sharp 
increase in the associated convection. A turn toward the north is 
forecast to begin later this afternoon as the system moves into a 
break in the Atlantic subtropical ridge pattern, with a general 
northward motion continuing through the remainder of the forecast 
period. The latest NHC model guidance is surprisingly in good 
agreement on this track scenario, with only minor forward speed 
differences noted between the models.

The 18-20 kt of westerly vertical wind shear affecting the 
depression is expected to abate somewhat during the next 12-24 
hours, which should allow for some slight strengthening to occur 
while the system moves over 27.5 deg C sea-surface temperatures. By 
48 hours, however, the shear is forecast to increase again in excess 
of 25 kt, which should act to weaken the cyclone, possibly even 
causing it to degenerate into a remnant low. For now, however, the 
official intensity forecast calls for the system to remain a 
tropical depression at days 3 and 4 in the event the cyclone 
regenerates at day 5 when the shear is forecast to decrease below 
10 kt, which may allow for convection to redevelop. The 
official intensity forecast closely follows a blend of the 
intensity consensus models IVCN and NOAA-HCCA.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0900Z 14.0N  49.9W   30 KT  35 MPH
 12H  28/1800Z 14.8N  50.3W   35 KT  40 MPH
 24H  29/0600Z 16.1N  50.3W   35 KT  40 MPH
 36H  29/1800Z 17.7N  50.2W   35 KT  40 MPH
 48H  30/0600Z 19.1N  50.0W   30 KT  35 MPH
 60H  30/1800Z 20.7N  49.7W   30 KT  35 MPH
 72H  31/0600Z 21.9N  49.7W   30 KT  35 MPH
 96H  01/0600Z 24.5N  50.5W   30 KT  35 MPH
120H  02/0600Z 27.5N  52.8W   30 KT  35 MPH
 
$$
Forecaster Stewart
 
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