[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 190839
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 AM AST MON SEP 19 2016

Karl continues to have a rather disorganized appearance in satellite
imagery.  The cloud pattern consists of a relatively small mass of
convection northeast of the center, with a separate shapeless
cluster of convection farther to the northeast.  The initial
intensity estimate is held at 35 kt in accordance with the Dvorak CI
number from TAFB.

Karl's current poor structure, proximity to an upper tropospheric
low near the Lesser Antilles, and large-scale subsidence/convergence
over the tropical Atlantic suggest that the storm should only slowly
strengthen during the next couple of days.  The intensity forecast
has been modified downward a bit further to reflect the likelihood
of a slower intensification.  After 72 hours, a notable increase in
moisture, waters of around 30 deg C, and low shear should promote
strengthening, perhaps more than indicated in this forecast.  The
intensity forecast during this time has been increased over the
previous one, and is closest to the LGEM model.

The initial motion estimate is 270/13. Karl should remain on the
south and southwest side of a subtropical ridge the next couple of
days, with the flow around this feature steering the cyclone
westward and then west-northwestward.  From days 3-5, Karl will
encounter a weakness in the ridge over the west-central Atlantic,
which should cause the cyclone to turn northwestward and northward
with a substantial decrease in forward speed.  The new track
forecast is nudged to the south of the previous one through 48
hours, with more emphasis put on the weaker GFS solution.  The track
forecast from days 3-5 has been adjusted to the east of the previous
one, and is consistent with the expectation of stronger cyclone as
depicted in the ECWMF solution.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 18.2N  47.7W   35 KT  40 MPH
 12H  19/1800Z 18.6N  49.7W   35 KT  40 MPH
 24H  20/0600Z 19.1N  52.1W   40 KT  45 MPH
 36H  20/1800Z 19.9N  54.6W   45 KT  50 MPH
 48H  21/0600Z 21.0N  57.1W   50 KT  60 MPH
 72H  22/0600Z 24.0N  62.2W   60 KT  70 MPH
 96H  23/0600Z 27.0N  65.2W   75 KT  85 MPH
120H  24/0600Z 29.5N  65.7W   85 KT 100 MPH

$$
Forecaster Kimberlain
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