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Subtropical Depression Four Discussion Number   4
NWS National Hurricane Center Miami FL       AL042020
1100 AM AST Tue Jun 23 2020
 
GOES-16 visible satellite imagery shows that the depression's
circulation has become better defined since yesterday, and the
center is exposed just to the north of a band of convection mainly
located within the southern semicircle.  This convection is aligned
along the Gulf Stream current, where instability is greatest, and
the system appears a little more tropical than yesterday.  However,
the depression is still collocated with an upper-level low, and it
will therefore retain the subtropical designation.  The initial
intensity remains 30 kt based on a ST1.5/25-30 kt classification
from TAFB.  A partial 1323 UTC ASCAT-B scatterometer pass showed
winds near 30 kt to the southeast of the center, and we'll continue
to monitor additional scatterometer data to see if there are winds
any higher than that.
 
The initial motion is still 11 kt, but the heading has turned
east-northeastward at 65 degrees.  The depression is forecast to
turn back toward the northeast by this evening and begin
accelerating on Wednesday within the prevailing mid-latitude flow.
This track will take the system over increasingly colder water,
placing it over sea surface temperatures less than 20 degrees
Celsius by early Wednesday.  Those ocean temperatures will make it
difficult to support deep convection, and the updated NHC forecast
now calls for the system to degenerate to a remnant low in 24 hours.
Dissipation has been moved to 48 hours, although global model
fields indicate that the system could open up into a trough by 36
hours before it moves past Newfoundland.
 
The Ocean Prediction Center has provided 12-ft sea radii in the
southern semicircle based on recent AltiKa and Jason-3 altimeter
data.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/1500Z 39.5N  62.1W   30 KT  35 MPH
 12H  24/0000Z 40.6N  60.3W   30 KT  35 MPH
 24H  24/1200Z 42.3N  58.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  25/0000Z 44.2N  55.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  25/1200Z...DISSIPATED
 
$$
Forecaster Berg
 
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