[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 170833
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 AM AST SAT SEP 17 2016

Karl is maintaining the status quo with its center at least 120
n mi to the southwest of the deep convection.  Since the ASCAT pass
from last evening showed a sizable area of 35-40 kt winds, and the
Dvorak estimates have been steady, the initial intensity remains 40
kt.  Karl is located just to the south of an upper-level low, and
the resultant westerly shear should gradually relax and change
direction during the next few days once Karl moves away from this
feature.  Sea surface temperatures will be steadily increasing along
Karl's forecast path, and mid-tropospheric moisture may begin to
increase after 48 hours.  Therefore, the NHC intensity forecast
continues to call for little change in intensity during the next 48
hours, followed by steady strengthening from day 3 to day 5.  This
forecast closely follows an average of the SHIPS and LGEM models
and still allows for the possibility of Karl becoming a hurricane
by day 5.

There is no doubt that the center of Karl has been losing latitude
during the past 6-12 hours, and the initial motion estimate is
265/12 kt.  A strengthening low- to mid-level ridge over the central
Atlantic is expected to continue pushing Karl south of due west
during the next 36 hours.  After that time, Karl will begin to
approach a weakness in the ridge located over the western Atlantic,
and the tropical cyclone is forecast to move west-northwestward on
days 3-5 well to the northeast of the Leeward Islands.  Although
there is some uncertainty on how far south Karl will get before it
turns west-northwestward, the spread among the track models is
actually quite small.  The updated NHC track forecast essentially
lies along the TVCN multi-model consensus line, which ends up being
a little south and west of the previous forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  17/0900Z 18.2N  38.2W   40 KT  45 MPH
 12H  17/1800Z 18.1N  40.1W   35 KT  40 MPH
 24H  18/0600Z 17.9N  42.8W   35 KT  40 MPH
 36H  18/1800Z 17.6N  45.4W   40 KT  45 MPH
 48H  19/0600Z 17.8N  47.9W   40 KT  45 MPH
 72H  20/0600Z 19.4N  53.1W   50 KT  60 MPH
 96H  21/0600Z 22.0N  58.5W   60 KT  70 MPH
120H  22/0600Z 24.5N  63.0W   70 KT  80 MPH

$$
Forecaster Berg
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