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TROPICAL STORM KARL DISCUSSION NUMBER  22
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
500 PM AST MON SEP 19 2016

Deep convection associated with Karl has increased during the day,
and the low-level center is now embedded beneath the convective
canopy.  Dvorak intensity estimates from TAFB and SAB increased to
T2.5/35 kt and T2.0/30 kt, respectively, but these numbers do not
yet support an increase in the initial intensity of 35 kt that has
been carried in the previous few advisories.  SHIPS and UW-CIMSS
shear analyses indicate that the southwesterly shear over Karl
remains 10-15 kt.  However, the guidance shows the shear decreasing,
and the improving structure of Karl suggests that this may be
already occurring.  In addition, moisture in the middle levels of
the atmosphere is expected to gradually increase, and SSTs will be
between 28-30C for the next five days.  All these ingredients
suggest that strengthening is likely, and the official forecast
continues to show intensification starting slowly at first and then
becoming faster after 48 hours.  This forecast is very close to a
consensus of the SHIPS and LGEM models, and the new official
forecast is essentially an update of the previous forecast.

The center of Karl jogged northwestward during the day, and the
long-term motion estimate is now west-northwestward, or 290/10 kt.
A west-northwestward motion is expected to continue for the next
couple of days while Karl moves along the southern edge of the
subtropical ridge.  After that time, Karl is forecast to reach the
western edge of the ridge and should turn northward and then
northeastward on days 4 and 5.  There is still some spread among
the track models when this turn is forecast to occur, and as a
result there is a lot of uncertainty on how much Karl will affect
Bermuda toward the end of the forecast period.  Still, the overall
guidance envelope has not shifted much, and the updated official
forecast is very close to the previous one.  This forecast is close
to the various consensus models, but it should be noted that the
GFS, GFS ensemble mean, and Florida Superensemble all show Karl
moving farther west before making the northward turn.

FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 19.3N  49.2W   35 KT  40 MPH
 12H  20/0600Z 19.8N  51.1W   40 KT  45 MPH
 24H  20/1800Z 20.6N  53.6W   40 KT  45 MPH
 36H  21/0600Z 21.6N  56.0W   45 KT  50 MPH
 48H  21/1800Z 22.9N  58.4W   50 KT  60 MPH
 72H  22/1800Z 25.9N  62.6W   60 KT  70 MPH
 96H  23/1800Z 29.0N  65.0W   75 KT  85 MPH
120H  24/1800Z 31.0N  63.0W   85 KT 100 MPH

$$
Forecaster Berg/Petersen/Chenard

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