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Subtropical Storm Joyce Discussion Number   4
NWS National Hurricane Center Miami FL       AL102018
1100 AM AST Thu Sep 13 2018

Joyce's satellite presentation is less than impressive this morning,
with the low-level center exposed to the northwest of a small patch
of deep convection. The initial intensity is set to 35 kt based on
the latest subtropical classification of ST2.5 from TAFB a 1208Z
ASCAT-B overpass that showed 30-35 kt winds north and northeast of
the center. Cyclone phase space diagrams still show Joyce with a
shallow-to-moderate warm core, and the system remains a subtropical
storm for now.

Little change in intensity is expected during the next few days, as
Joyce will continue to be affected by strong westerly-to-
southwesterly vertical wind shear. The new NHC forecast is a little
below the intensity consensus given the weakening trend seen in the
global models. Dissipation is shown at 96 hours, but it wouldn't be
surprising if Joyce becomes a post-tropical cyclone before that.

The initial motion estimate is 245/05. Joyce is currently situated
a little to the west of an upper-level low, which is currently
steering the system southwestward and southward, and that should
continue for the next day or so. Then, Joyce should begin to
accelerate northeastward ahead of an approaching mid-level trough.
The new NHC track forecast follows the trend of the latest
guidance, and is a little to the west of the previous one through
36 hours. The official forecast is close to the latest HCCA and
TVCA consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 33.7N  43.7W   35 KT  40 MPH
 12H  14/0000Z 33.1N  44.1W   35 KT  40 MPH
 24H  14/1200Z 32.2N  44.4W   40 KT  45 MPH
 36H  15/0000Z 31.9N  44.0W   40 KT  45 MPH
 48H  15/1200Z 32.5N  42.6W   40 KT  45 MPH
 72H  16/1200Z 35.5N  38.5W   35 KT  40 MPH
 96H  17/1200Z...DISSIPATED

$$
Forecaster Brennan

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