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TROPICAL STORM KARL DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 AM AST FRI SEP 16 2016

Water vapor satellite imagery indicates that Karl is moving directly
toward the base of a mid-/upper-level trough while being affected by
at least 20 kt of westerly shear.  A recent SSMIS microwave pass
showed that the deep convection remains displaced to the northeast
of the center.  Since the structure of the cyclone has not changed
since the last advisory, the initial intensity is held at 40 kt.

The SSMIS data indicated that the center has moved a little north of
previous position estimates, and the initial motion is now 280/11
kt.  Karl may gain a little more latitude during the next 12-24
hours, but after that time a strong subtropical ridge is expected to
force the cyclone to move south of due west or possibly west-
southwestward between 36-48 hours.  Once it reaches the western
portion of the ridge and intensifies, Karl is likely to again gain
some latitude, turning west-northwestward by days 4 and 5.  The
track models all agree on this scenario and keep Karl well to the
east and northeast of the Leeward Islands during the five-day
forecast period.  Mainly because of the adjustment in the initial
position, the new NHC track forecast is a little north of the
previous forecast, and it lies closest to an average of the GFS and
ECMWF solutions.

Strong to moderate vertical shear is expected to persist for the
next 24-36 hours, and little to no change in strength is anticipated
during that time.  Even after 36 hours, Karl will be moving through
a dry environment over the central tropical Atlantic, but lower
shear and warming sea surface temperatures could allow for at least
gradual strengthening.  The intensity models have trended a little
bit higher at the end of the forecast period, and the new NHC
forecast shows Karl potentially reaching hurricane intensity by day
5.  This forecast is very close to the SHIPS and LGEM models.

The initial 12-ft sea radii have been expanded considerably on this
advisory based on recent altimeter wave height data.

FORECAST POSITIONS AND MAX WINDS

INIT  16/0900Z 18.3N  33.4W   40 KT  45 MPH
 12H  16/1800Z 18.7N  35.3W   40 KT  45 MPH
 24H  17/0600Z 18.7N  38.0W   40 KT  45 MPH
 36H  17/1800Z 18.3N  40.7W   40 KT  45 MPH
 48H  18/0600Z 17.7N  43.3W   45 KT  50 MPH
 72H  19/0600Z 17.6N  48.1W   50 KT  60 MPH
 96H  20/0600Z 19.0N  53.0W   55 KT  65 MPH
120H  21/0600Z 21.5N  57.5W   65 KT  75 MPH

$$
Forecaster Berg

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