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Tropical Storm KARL Forecast Discussion


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000
WTNT42 KNHC 242041
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  42
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 PM AST SAT SEP 24 2016

The convective pattern of Karl has become less organized today and
currently resembles a shear pattern, which isn't surprising given
the 35 kt of southwesterly shear analyzed over Karl by UW-CIMSS.  A
GPM overpass from earlier today showed that the inner-core structure
of the cyclone had degraded, and this was also noted by the last
aircraft flight this morning.  The initial intensity remains 55 kt
based on the latest Dvorak Data-T numbers of T3.5/55 kt from TAFB
and SAB.  A NOAA Hurricane Hunter aircraft is en route to sample
Karl and provide more data on its current intensity and structure.
Karl is expected to strengthen during the next 12 to 24 hours, but
much of this will be due to baroclinic effects as the cyclone will
be under very high shear and moving over cooler SSTs. The NHC
forecast shows Karl reaching 70 kt at 24 h as a post-tropical
cyclone based on the GFS and ECMWF guidance.  Karl should be
absorbed by a larger extratropical low over the north Atlantic by 36
h, as indicated by global model fields.

The initial motion estimate is 055/20.  Karl should continue to
accelerate on an east-northeastward to northeastward heading ahead
of a broad deep-layer trough until the cyclone is absorbed, and the
forward speed is expected to be near 50 kt by 24 hours.  The new
NHC track forecast is an update of the previous one and remains near
the middle of the tightly packed guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  24/2100Z 33.6N  61.1W   55 KT  65 MPH
 12H  25/0600Z 36.4N  55.3W   60 KT  70 MPH
 24H  25/1800Z 41.9N  45.1W   70 KT  80 MPH...POST-TROPICAL
 36H  26/0600Z...DISSIPATED

$$
Forecaster Brennan