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Subtropical Storm OSCAR


Subtropical Storm Oscar Discussion Number   4
NWS National Hurricane Center Miami FL       AL162018
500 PM AST Sat Oct 27 2018

Oscar is still located beneath an upper-level low, however it its
convective structure is now more reminiscent of a tropical cyclone.
Deep convection is primarily occuring in a small burst just south
of the center of Oscar, however this convective activity appears to
be displaced by light northerly shear associated with the upper-low.
Earlier AMSU sounding data indicated that the cyclone has developed
a weak but vertically deep warm core which also indicates that Oscar
is nearly a tropical cyclone, if it isn't one already. Oscar is
moving quickly westward away from the upper-low, and will likely
become a tropical storm later tonight if its current structural
trends continue.

The initial intensity is held at 50 kt, based primarily on the
latest Hebert-Poteat subtropical intensity estimate from TAFB. The
intensity guidance has bounced back, and the most of the intensity
guidance is higher than it was six hours ago. While little change
was made to the NHC intensity forecast, it now lies very near the
intensity consensus at all forecast hours. Gradual intensification
is still expected and Oscar is forecast to approach hurricane
strength by Monday. Slight additional intensification is possible
through the middle of next week, until extratropical transition
occurs by 120 h.

Oscar moved very quickly westward this afternoon, but a more
representative motion estimate is 265/15 kt. The latest runs of the
typically reliable global models are in better agreement than they
were this morning. Oscar is forecast to move west-southwestward or
westward for the next day or two on the south side of a mid-level
ridge to the north. The cyclone is then expected to recurve and
accelerate northeastward ahead of a substantial mid-latitude trough
moving across the western and central Atlantic by the middle of next
week. The official track forecast has been adjusted westward to
bring it closer to the latest track consensus, especially for the
first 72 h of the forecast. By day 5, the official forecast is quite
similar to the previous advisory, but with a slightly slower forward
speed for Oscar.


INIT  27/2100Z 26.9N  50.7W   50 KT  60 MPH
 12H  28/0600Z 26.1N  53.0W   50 KT  60 MPH...TROPICAL CYCLONE
 24H  28/1800Z 25.7N  55.8W   55 KT  65 MPH
 36H  29/0600Z 25.6N  57.9W   55 KT  65 MPH
 48H  29/1800Z 26.4N  59.1W   60 KT  70 MPH
 72H  30/1800Z 30.6N  57.5W   70 KT  80 MPH
 96H  31/1800Z 38.5N  50.0W   70 KT  80 MPH
120H  01/1800Z 46.5N  38.0W   60 KT  70 MPH...POST-TROP/EXTRATROP

Forecaster Zelinsky