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Subtropical Storm OSCAR


Subtropical Storm Oscar Discussion Number   1
NWS National Hurricane Center Miami FL       AL162018
1100 PM AST Fri Oct 26 2018

Satellite imagery and scatterometer data indicate the circulation
of the broad low pressure area over the central Atlantic has become
better defined, with a low-level center developing to the south of
a convective burst.  The scatterometer data indicate 35-40 kt winds
about 70-90 n mi from the center, and satellite imagery shows that
the cyclone is entangled with a developing upper-level low.  Based
on these factors, advisories are being initiated on the latest in
this year's series of subtropical storms, Oscar.

Due to the recent development of the center, the initial motion is
an uncertain 335/8.  The track guidance is in excellent agreement
that Oscar should should turn sharply westward and west-
southwestward during the next 24 h as it pivots around the north
side of the upper-level low, with this general motion continuing
through about 48 h.  After that, the cyclone should turn more
westward at a slower forward speed as it approaches a weakness in
the subtropical ridge.  A northeastward motion appears likely from
72-120 h due to a mid-latitude trough approaching Oscar from the
west.  However, there are significant differences in the forward
speed between the GFS, ECMWF, and UKMET models that make this part
of the forecast low confidence.  Overall, the forecast track is
close to the TVCN consensus model, and it splits the difference
between the divergent global models late in the forecast period.

Gradual strengthening is forecast as Oscar remains in the deep-layer
cyclonic flow of the upper-level low during the first 36-48 h.
After that time, the global models suggests the system will have a
chance to develop a tropical cyclone outflow pattern, and based on
this the forecast calls for Oscar to become a tropical cyclone near
the 48 h point.  Interaction with the aforementioned mid-latitude
trough may allow some additional intensification before Oscar
encounters stronger shear near the 120 h point.  The FV3 model shows
a much weaker Oscar than the other dynamical models, and it is
possible that dry air entrainment may hamper development through
the forecast period.  Thus, the intensity forecast is below the
intensity consensus and on the weaker side of the intensity


INIT  27/0300Z 26.7N  45.7W   40 KT  45 MPH
 12H  27/1200Z 27.2N  47.2W   45 KT  50 MPH
 24H  28/0000Z 26.6N  50.3W   50 KT  60 MPH
 36H  28/1200Z 25.6N  53.2W   50 KT  60 MPH
 48H  29/0000Z 25.3N  55.3W   55 KT  65 MPH...TROPICAL CYCLONE
 72H  30/0000Z 26.5N  57.5W   60 KT  70 MPH
 96H  31/0000Z 30.0N  55.5W   60 KT  70 MPH
120H  01/0000Z 34.0N  50.0W   55 KT  65 MPH

Forecaster Beven