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Subtropical Storm OSCAR


Subtropical Storm Oscar Discussion Number   3
NWS National Hurricane Center Miami FL       AL162018
1100 AM AST Sat Oct 27 2018

Oscar's organization has improved this morning. Although the
subtropical storm is still entangled with an upper-level low,
convection has increased near the center of the cyclone since last
night. The most recent Hebert-Poteat subtropical intensity estimate
from TAFB has increased accordingly to 45-50 kt. Furthermore,
Canadian drifting buoy 47546 recently reported a minimum pressure of
just below 996 mb to the east of Oscar's center, suggesting the
central pressure of the cyclone has decreased since the last
advisory. The initial intensity is therefore increased to 50 kt for
this advisory.

Little change has been made to the intensity forecast. The GFS and
many of its associated models (HWRF, DSHP, LGEM) have changed
abruptly and forecast far less intensification than they did just 6
hours ago. However, the CTCI, HMON, and ECMWF-based statistical
guidance still show Oscar reaching hurricane strength within a few
days. Rather than chase a possible short-term trend in the intensity
guidance, the official intensity forecast will stay the course for
now and is a little above the intensity consensus, bringing Oscar to
hurricane strength in around 48 h. After that time, some slight
additional intensification is possible, but Oscar is ultimately
expected to undergo extratropical transition by the end of the
forecast period, which should cause the cyclone to steadily weaken.

Oscar has turned toward the west and the initial motion estimate is
now 270/11 kt. A west-southwestward motion is anticipated later
today as Oscar moves around the back side of an mid- to upper-level
trough over the central Atlantic, followed by a turn toward the west
on the south side of a subtropical ridge to the north. As long as
Oscar intensifies as forecast, it should turn sharply northeastward
early next week ahead of a mid-latitude trough advancing across the
western and central Atlantic, and then accelerate in that direction
while undergoing extratropical transition. The GFS is an outlier,
showing a much weaker and vertically shallow cyclone that does not
fully recurve, but all of the other global models are in generally
good agreement with the scenario listed above. Despite the
inconsistency of the GFS, the model consensus has not changed
significantly since the last advisory, so only minor adjustments
were made to the NHC track forecast.


INIT  27/1500Z 27.3N  48.4W   50 KT  60 MPH
 12H  28/0000Z 26.9N  50.6W   55 KT  65 MPH
 24H  28/1200Z 26.2N  53.5W   60 KT  70 MPH...TROPICAL CYCLONE
 36H  29/0000Z 25.9N  56.1W   60 KT  70 MPH
 48H  29/1200Z 26.5N  57.4W   65 KT  75 MPH
 72H  30/1200Z 30.2N  57.0W   70 KT  80 MPH
 96H  31/1200Z 37.0N  50.0W   70 KT  80 MPH
120H  01/1200Z 47.0N  38.0W   60 KT  70 MPH...POST-TROP/EXTRATROP

Forecaster Zelinsky