[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 301435
TCDAT1

Hurricane Oscar Discussion Number  15
NWS National Hurricane Center Miami FL       AL162018
1100 AM AST Tue Oct 30 2018

Cloud-top temperatures have warmed a bit overall, and the convective
pattern is becoming more asymmetric as dry air is infiltrating the
southern and eastern part of Oscar's circulation.  However, the
hurricane is still producing plenty of inner-core convection and
some lightning strikes.  Dvorak Current Intensity numbers from TAFB
and SAB still support maximum winds of 90-100 kt, but objective
numbers are much lower (65-75 kt), so Oscar's initial intensity is
lowered slightly to 85 kt.

Increasing shear and stronger upper-level divergence will likely
offset each other in the short term, causing Oscar to maintain its
intensity or only slightly weaken during the next 24 hours.
However, a cold front is quickly approaching Oscar from the
northwest, and their interaction is expected to cause Oscar to
complete extratropical transition and become fully embedded within
the frontal zone in about 36 hours.  Oscar's winds should gradually
diminish after it becomes extratropical, but the NHC official
forecast remains above the various consensus aids from 36 hours and
beyond and lies closest to the GFS and ECMWF global models, which
should have a good handle on the cyclone's structure during the
post-tropical phase.

Oscar continues to accelerate and has turned north-northeastward,
or 020/12 kt, while entering the flow between a large high over the
eastern/central Atlantic and a mid-latitude trough now moving over
the western Atlantic.  Oscar is expected to become embedded within
the trough by 36 hours (the completion of extratropical transition),
with the entire system becoming a cut-off low north of the jet
stream by days 4 and 5.  The track models are in fairly good
agreement on Oscar's future path, but there are speed differences
by the end of the forecast period.  Of particular note, the ECMWF
is much faster than the other models, showing a more progressive
pattern on day 5.  The NHC track forecast lies close to the
previous official forecast to maintain continuity, but it is still
faster than the GFS, HWRF, and the TVCN multi-model consensus at
day 5.

Large swells from Oscar will affect Bermuda through Wednesday.
Please consult products from your local weather office as these
conditions could cause life-threatening surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 29.7N  57.7W   85 KT 100 MPH
 12H  31/0000Z 31.8N  56.1W   80 KT  90 MPH
 24H  31/1200Z 35.6N  52.6W   80 KT  90 MPH
 36H  01/0000Z 40.6N  48.7W   75 KT  85 MPH...POST-TROP/EXTRATROP
 48H  01/1200Z 45.1N  44.4W   65 KT  75 MPH...POST-TROP/EXTRATROP
 72H  02/1200Z 52.6N  31.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  03/1200Z 59.0N  18.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  04/1200Z 63.5N   6.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg
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