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POST-TROPICAL CYCLONE KARL DISCUSSION NUMBER  45
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 AM AST SUN SEP 25 2016

While Karl was producing a large shield of deep convection earlier,
the convective tops have since warmed substantially and decreased in
coverage. The cyclone's cloud pattern resembles a baroclinic leaf,
which is the typical satellite signature of a system that has become
a frontal wave.  The leading edge of a stratocumulus cloud deck,
indicative of cold-air advection, is also encroaching on the
low-level center.  Based on these developments and FSU Phase Space
diagrams that already show the cyclone as cold core, Karl is being
declared an extratropical cyclone. The initial intensity estimate is
held at 60 kt in agreement with earlier Global Hawk sonde data and
the cyclone's rapid translational speed.  Global models show Post-
Tropical Karl being absorbed by a larger extratropical storm over
the North Atlantic after about 24 hours.

A series of earlier microwave images showed that the center was
rapidly becoming deformed due to nearly 50 kt of southwesterly
shear.  Since this has made finding the location of the low-level
center difficult, the initial motion estimate is a rather uncertain
055/42.  The post-tropical cyclone is expected to accelerate a bit
further toward the northeast and then turn north-northeast before
losing its identity.


FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 39.9N  47.9W   60 KT  70 MPH...POST-TROP/EXTRATROP
 12H  26/0000Z 45.0N  39.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 24H  26/1200Z 52.5N  31.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 36H  27/0000Z...ABSORBED

$$
Forecaster Kimberlain

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