[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 210835
TCDAT2

TROPICAL DEPRESSION KARL DISCUSSION NUMBER  28
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 AM AST WED SEP 21 2016

Karl's structure is very difficult to determine this morning.
Satellite data indicate that the low-level center moved westward
far away from the convection, and currently it is hard to say if
Karl possess a closed circulation or not. Assuming that it still
does, the maximum winds are estimated generously at 30 kt, since the
cloud pattern has become less organized. I would not be surprised if
early visible satellite images will reveal that the cyclone has
degenerated into a broad area of low pressure.

Global models have totally failed so far in forecasting the
upper-level winds surrounding Karl. The upper-low near Karl which
unanimously all models have been forecasting to weaken is still
strong and producing shear over the cyclone. Given such a resilient
shear pattern, additional weakening is anticipated today. However,
most of the models are still predicting a favorable pattern for
intensification, and on this basis as well as continuity, the NHC
forecast calls for some strengthening beyond 36 hours while Karl
moves away from the hostile tropics. By the end of the forecast
period, Karl should be rapidly losing tropical characteristics
while it interacts with the mid-latitude flow.

The initial motion is also highly uncertain, giving that we have
been following the low-cloud swirl defining the alleged center. The
best estimate is toward the west or 280 degrees at 12 kt. Karl is
approaching the southwestern edge of the subtropical ridge, and this
pattern should result in a turn to the northwest and then north
during the following two days. After that time, a sharp recurvature
is anticipated around the northwestern portion of the subtropical
high and ahead of a mid-latitude shortwave. This sharp recurvature
is the solution provided by most of the track models, and the NHC
forecast is in the middle if the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0900Z 20.2N  57.6W   30 KT  35 MPH
 12H  21/1800Z 20.9N  59.3W   25 KT  30 MPH
 24H  22/0600Z 23.0N  61.5W   30 KT  35 MPH
 36H  22/1800Z 25.0N  64.0W   35 KT  40 MPH
 48H  23/0600Z 27.0N  65.5W   45 KT  50 MPH
 72H  24/0600Z 30.0N  64.0W   60 KT  70 MPH
 96H  25/0600Z 35.5N  56.5W   75 KT  85 MPH
120H  26/0600Z 43.0N  42.0W   65 KT  75 MPH...POST-TROP/EXTRATROP

$$
Forecaster Avila
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