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Tropical Depression Fifteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL152020
500 PM EDT Mon Aug 31 2020
 
Satellite images indicate that the area of low pressure offshore of
the Carolinas has had convection organized in bands since before
dawn, and scatterometer plus an Air Force Reserve Hurricane
Hunter mission data confirm that the circulation is closed.  Thus,
this is now a tropical depression, and the initial wind speed is
set to 30 kt in accordance with 25-30 kt ASCAT-A data plus buoy
42001 readings which earlier had an adjusted 10-m peak of 30 kt.
 
The depression is moving northeastward at about 10 kt.  The system 
should gradually turn toward the east-northeast by Wednesday due to 
it moving around the northwest side of the subtropical ridge, then 
move eastward in a few days around the flat ridge.  By late week, 
the cyclone could slow and eventually turn back toward the northeast 
around a rather strong mid-latitude high pressure system over the 
northeast Atlantic.  There is considerable spread in the guidance, 
which really seems to depend upon whether the system stays coherent, 
like the official forecast, or would become a shallow low-level 
swirl by 120h and end up slower and south of forecast track. This 
forecast is near the corrected-consensus guidance, leaning toward 
the ECMWF-based models, and it should be considered of low 
confidence.
 
Gradual strengthening is expected over the next day or so while the 
depression remains in a low-to-moderate shear environment. Although 
the depression is expected to be traversing the warm Gulf Stream for 
the next several days, wind shear is expected to greatly increase by 
Wednesday, which should limit intensification.  In fact there's 
some chance the system could decay and lose any deep convection in 
rather strong shear in a few days. However, since it likely will be 
moving near the Gulf Stream, I suspect it will continue to pulse 
thunderstorm activity and stay alive throughout the period. The NHC 
intensity forecast is near or just above the model consensus on 
that reasoning, closest to the HWRF model.  The cyclone could 
become extratropical (or a remnant low) by the end of the forecast, 
but this is very uncertain.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/2100Z 32.6N  76.5W   30 KT  35 MPH
 12H  01/0600Z 33.8N  75.0W   35 KT  40 MPH
 24H  01/1800Z 34.9N  72.4W   40 KT  45 MPH
 36H  02/0600Z 35.8N  69.7W   40 KT  45 MPH
 48H  02/1800Z 36.7N  67.0W   40 KT  45 MPH
 60H  03/0600Z 37.6N  63.7W   35 KT  40 MPH
 72H  03/1800Z 38.2N  60.5W   35 KT  40 MPH
 96H  04/1800Z 39.0N  55.0W   35 KT  40 MPH
120H  05/1800Z 41.5N  49.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Blake
 
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