[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 172034
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 PM AST SAT SEP 17 2016

Convection continues to flare up and down near the center of Karl,
with a larger mass well to the northeast of the center.  In
addition, the circulation looks more elongated than earlier today,
perhaps due to the convective asymmetry.  The initial wind speed is
held at 40 kt since the system does not look all that different,
although the satellite classifications are a bit lower.

Karl could still weaken a little bit in the short term while the
cyclone is in a recovery stage from its interaction with an
upper-level low. Gradual strengthening is then forecast by early
next week as the storm encounters very warm water, low shear, and a
marginal moisture environment.  Model guidance is very similar to
the previous cycle, except for the ECMWF which shows a more powerful
cyclone by day 5.  Very little change was made to the official
forecast, which continues to be most similar to a blend of the
SHIPS/LGEM models.

The initial motion estimate is unchanged from the previous one,
265/11.  Karl should begin to gain some latitude by Monday as it
moves around the southern side of the subtropical ridge.  A
west-northwestward motion is forecast to begin on Tuesday due to
the orientation of the ridge, and this motion could continue for
the rest of the 5-day period.  The biggest change since the last
cycle is that model guidance is showing a stronger ridge in the
central Atlantic, which would prolong the west-northwestward
motion.  The track models have shifted westward at long range, and
the official forecast is moved in that direction, but not as far
west as the 12Z ECMWF/GFS solutions.

FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 18.1N  40.4W   40 KT  45 MPH
 12H  18/0600Z 17.9N  42.3W   35 KT  40 MPH
 24H  18/1800Z 17.8N  45.0W   40 KT  45 MPH
 36H  19/0600Z 18.1N  47.6W   40 KT  45 MPH
 48H  19/1800Z 18.8N  50.3W   45 KT  50 MPH
 72H  20/1800Z 20.6N  55.4W   50 KT  60 MPH
 96H  21/1800Z 23.0N  60.5W   60 KT  70 MPH
120H  22/1800Z 25.0N  64.5W   70 KT  80 MPH

$$
Forecaster Blake

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