[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 220240
TCDAT2

TROPICAL DEPRESSION KARL DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 PM AST WED SEP 21 2016

While the convection associated with Karl has become more
concentrated to the northwest of the center during the past several
hours, dropsonde data from the NOAA G-IV jet indicates that the
cyclone's circulation is at least somewhat disorganized.  A closed
circulation exists from the surface to 700 mb.  Above that, there is
a poorly defined trough at 500 and 400 mb with southwesterly winds
of 10-15 kt above the low level center. Finally, the flow at 300 and
200 mb is from the east and southeast. The maximum surface winds in
the dropsonde data were 25 kt, and recent ASCAT data implies
maximum winds near 30 kt.  Thus, the initial intensity remains 30
kt.

The initial motion is 315/13 as Karl continues to move between the
southwestern periphery of subtropical ridge and a upper- to
mid-level low located north of Puerto Rico.  This northwestward
track should continue for another 24 hours or so.  Beyond that time,
Karl should turn northward, move through a break in the ridge, and
then accelerate northeastward as it becomes embedded in the
westerlies. Since the last advisory, the track guidance has shifted
a little to the east during the first 72 hours, and the new forecast
track for that period lies between the model consensus and the
previous forecast.  After recurvature, there remain some differences
in the guidance regarding the forward speed of Karl, and the
forecast track is in best agreement with a blend of the GFS and
HWRF models.

While the vertical shear is forecast to gradually decrease over
Karl, mid-level moisture values to the southwest of the cyclone
remain marginal according to the NOAA jet data.  In addition, the
disorganized circulation argues against any rapid strengthening.
The intensity forecast calls for slow intensification for the next
36 hours, followed by faster strengthening until the 72 hour point
when the cyclone is forecast to be a hurricane.  Karl should weaken
as it begins extratropical transition between 72-96 hours, with the
transition to a storm-force extratropical low being complete by 120
hours.


FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 22.9N  59.6W   30 KT  35 MPH
 12H  22/1200Z 24.2N  61.3W   35 KT  40 MPH
 24H  23/0000Z 25.9N  63.4W   40 KT  45 MPH
 36H  23/1200Z 27.6N  64.3W   45 KT  50 MPH
 48H  24/0000Z 29.7N  64.1W   55 KT  65 MPH
 72H  25/0000Z 33.5N  58.5W   70 KT  80 MPH
 96H  26/0000Z 40.0N  47.0W   70 KT  80 MPH
120H  27/0000Z 47.5N  33.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven
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