000
WTNT42 KNHC 160256
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 PM AST THU SEP 15 2016

During the past six hours, a significant increase in the amount and
the organization of the deep convection has occurred near and over
the well-defined low-level circulation center. The southwestern edge
of the cold cloud canopy, characterized by tops as cold as -89C, has
continued to expand southwestward over the center despite
southwesterly vertical wind shear of 20-25 kt. The initial intensity
has been increased to 40 kt based on a constrained Dvorak satellite
estimate of 35 kt form TAFB, but with a data T-number of T3.0/45 kt
using a shear pattern. A 15/2247Z partial ASCAT-B pass indicated
several 35-36 kt surface wind vectors in the northeastern quadrant
more than 60 nmi from the center. Based on continued improvement in
the satellite presentation since the ASCAT pass, the initial
intensity is set at 40 kt, making Karl the eleventh named storm of
the season.

Karl is moving westward or 275/11 kt. The cyclone is expected to
move westward and then west-southwestward around a strengthening
Atlantic subtropical ridge for the next 48-72 hours. After that
time, the ridge is forecast to weaken some, allowing Karl to turn
back toward the west and then west-northwest by day 5. The new NHC
forecast is essentially on top of the previous advisory track, and
lies close to the multi-model consensus TVCX and the Florida State
Superensemble model.

Karl is expected to remain in a moderate to strong vertical wind
shear environment for the next 36 hours or so, which should inhibit
significant intensification. After that time, however, the shear is
forecast to decrease to around 5 kt for the remainder of the
120-h period. That would normally result in more robust
strengthening while the cyclone is moving over 28-29C SSTs.
However, Karl will also be moving through a very dry mid-level
moisture regime during that time, so the intensification trend is
forecast to be much slower than the climatological rate of 20 kt
per day, and lies close to the SHIPS intensity forecast.

The large 34-kt wind radius in the northeastern quadrant is based on
the aforementioned ASCAT wind data.

FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 17.9N  32.5W   40 KT  45 MPH
 12H  16/1200Z 18.0N  34.5W   40 KT  45 MPH
 24H  17/0000Z 18.0N  37.1W   40 KT  45 MPH
 36H  17/1200Z 17.8N  39.7W   40 KT  45 MPH
 48H  18/0000Z 17.5N  42.4W   45 KT  50 MPH
 72H  19/0000Z 17.1N  47.8W   50 KT  60 MPH
 96H  20/0000Z 17.8N  52.7W   55 KT  65 MPH
120H  21/0000Z 19.0N  57.0W   60 KT  70 MPH

$$
Forecaster Stewart