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TROPICAL STORM KARL DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM AST MON SEP 19 2016

Visible satellite imagery shows Karl consists of a swirl of low
clouds with nearly all of the associated deep convection located to
the northeast of the exposed low-level center.  The structure has
changed relatively little from six hours ago, and the initial wind
speed remains 35 kt based on the Dvorak Current Intensity estimate
from TAFB.

Karl is still being affected by 10-15 kt of southwesterly vertical
shear, and with the mid-level relative humidity in the surrounding
environment only 40-50 percent, the cyclone continues to struggle
to produce deep convection near its center and over the western
part of the circulation.  However, the SHIPS guidance indicates
that the shear should continue to decrease during the next few
days, and mid-level moisture is likely to increase over 60 percent
by day 3.  Therefore, only slight strengthening is anticipated
during the next 48 hours, but that should be followed by quicker
intensification on days 3-5, with Karl still expected to reach
hurricane intensity by the end of the forecast period.  The updated
official intensity forecast is very close to the SHIPS guidance for
the entire forecast period, and it is just slightly below the
previous forecast after 24 hours.

The initial motion is just a little slower at 275/11 kt.  Karl's
westward motion is the result of it being positioned south of the
Bermuda-Azores high.  However, the cyclone is expected to reach a
break in the ridge located over the western Atlantic in a few days,
which will cause it to turn northwestward by day 3 and then
northward by day 5.  The track models are tightly clustered through
day 3 before Karl makes its turn, but there is more spread on days
4 and 5 regarding where the turn will occur.  The GFS and GFS
ensemble mean both take Karl farther west before it turns toward
the north, while the bulk of the other models make the turn east of
the previous forecast track.  For the sake of continuity, the
updated official track forecast is very similar to the previous
forecast, and it lies relatively close to a consensus of the GFS
and ECMWF models.

FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 18.6N  48.3W   35 KT  40 MPH
 12H  20/0000Z 18.9N  50.3W   35 KT  40 MPH
 24H  20/1200Z 19.5N  52.8W   40 KT  45 MPH
 36H  21/0000Z 20.4N  55.2W   40 KT  45 MPH
 48H  21/1200Z 21.6N  57.7W   45 KT  50 MPH
 72H  22/1200Z 24.5N  62.3W   55 KT  65 MPH
 96H  23/1200Z 27.5N  65.5W   70 KT  80 MPH
120H  24/1200Z 29.5N  65.0W   80 KT  90 MPH

$$
Forecaster Berg

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