[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 290245
TCDAT1

Hurricane Oscar Discussion Number   9
NWS National Hurricane Center Miami FL       AL162018
1100 PM AST Sun Oct 28 2018

Satellite imagery indicates that the structure of Oscar has changed
little over the past several hours.  Microwave imagery has shown a
ring or eye feature which is at least partly encircled by deep
convection, and an eye has made occasional appearances in infrared
imagery.  Satellite intensity estimates have changed little, so the
initial intensity remains 65 kt.  One change from the previous
advisory is that recent scatterometer data show that Oscar has
smaller 34-kt wind radii than previously thought, so the initial
and forecast wind radii have been modified.

The initial motion remains 270/14.  Oscar is approaching the
western end of a large low- to mid-level ridge over the central
Atlantic, and thus it should turn northwestward with a decrease in
forward speed during the next 24 h or so.  From 24-72 h, the
hurricane should recurve into the mid-latitude westerlies on the
east side of a deep-layer trough moving eastward through the western
and central Atlantic.  The models are in good agreement on the
forecast track through 72 h, then show significant differences based
on whether Oscar merges with a new cut-off low pressure area over
the central Atlantic or remains a separate system in the westerlies.
The latest GFS has joined the UKMET in showing Oscar racing
northeastward into the northeastern Atlantic by 120 h as a separate
system.  In contrast, the HWRF and the FV3 models show a sharp turn
toward the south as the new low captures Oscar.  The ECMWF is
between these extremes in showing a more gradual turn toward the
east well to the east of the HWRF/FV3 and well to the southwest of
the GFS/UKMET.  The new forecast track is a little west of the
previous track in the early part of the forecast based on the
current position and motion. Later in the forecast period, it has
been shifted a little to the east in best agreement with the ECMWF.

Oscar is forecast to remain in a moist and unstable environment for
the next 36-48 h, and the trough approaching from the west is
likely to create a divergent outflow pattern.  Based on this, the
intensity forecast now shows a faster rate of strengthening than
the previous advisory.  After reaching its peak intensity in 36-48
h, it appears likely that the extratropical transition will occur
near the 72 h point before the winds drop below hurricane force.
After transition, Oscar is expected to gradually decay.  It should
be noted that if the FV3 scenario verifies, Oscar may maintain
tropical cyclone status beyond 72 h.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 25.6N  57.0W   65 KT  75 MPH
 12H  29/1200Z 25.9N  58.3W   70 KT  80 MPH
 24H  30/0000Z 27.1N  59.0W   80 KT  90 MPH
 36H  30/1200Z 29.1N  58.3W   85 KT 100 MPH
 48H  31/0000Z 32.0N  56.0W   85 KT 100 MPH
 72H  01/0000Z 39.0N  48.5W   75 KT  85 MPH...POST-TROP/EXTRATROP
 96H  02/0000Z 44.0N  38.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  03/0000Z 45.0N  29.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven
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