[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 240252
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  39
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 PM AST FRI SEP 23 2016

A few hours ago, a NOAA Hurricane Hunter aircraft reported
flight-level winds of 71 kt at 7800 ft about 30 n mi to the
southwest of the center, along with SFMR surface wind estimates of
near 55 kt.  The minimum central pressure at the time was near 990
mb.  Since then, the cyclone has gotten better organized, with
radar data from Bermuda showing a strong convective band west and
northwest of the center.  One caveat to the increased organization
is that the center apparent in both radar and microwave imagery may
be a little to the northwest of the surface center.  Based on the
earlier aircraft data, the initial intensity is set to 55 kt, and
this could be a little conservative.

Karl is expected to remain over sea surface temperatures of between
29-30C for the next 12-24 hours or so in an environment of moderate
vertical wind shear.  This should allow the cyclone to strengthen
to a hurricane in about 24 hours. After that, the cyclone should
undergo extratropical transition as it merges with the cold front,
and this should be complete by 48 hours.  The cyclone is likely to
be absorbed by a larger extratropical low between 48-72 hours.  The
new intensity forecast is similar to the previous forecast, but it
lies a little below the forecasts of the SHIPS and LGEM models.

The initial motion is 020/11.  Karl is about to enter strong
southwesterly flow in advance of a deep-layer trough and associated
surface cold front moving eastward from the northeastern United
States.  This should result in a turn toward the northeast during
the next several hours and an increase in forward speed.  The new
track forecast has changed little from the previous forecast, and
calls for Karl to make its closest approach to Bermuda during the
next 12 hours and then move rapidly away from the island.  Overall,
the forecast track is near the center of the tightly clustered
guidance.

The wind radii have been revised based on a recent scatterometer
overpass and input from the Ocean Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z 30.8N  65.1W   55 KT  65 MPH
 12H  24/1200Z 32.5N  63.0W   60 KT  70 MPH
 24H  25/0000Z 35.5N  57.8W   70 KT  80 MPH
 36H  25/1200Z 39.5N  49.9W   70 KT  80 MPH
 48H  26/0000Z 45.0N  40.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 72H  27/0000Z...ABSORBED BY LARGER EXTRATROPICAL LOW

$$
Forecaster Beven
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