[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 211443
TCDAT2

TROPICAL DEPRESSION KARL DISCUSSION NUMBER  29
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM AST WED SEP 21 2016

A research flight by the NOAA P3 aircraft earlier this morning had
a difficult time closing off a well-defined center of circulation.
However, we are able to track what looks like a reasonable center
on early-morning visible satellite imagery.  Based on the latest
satellite images and the P3 data, it does appear that the center
has wobbled toward the northwest and slowed down a bit.  However,
the longer-term 12-hour motion estimate is still west-northwestward,
or 295/8 kt.  Most of the deep convection remains displaced well to
the east of the center, but new convection has recently been
developing just to the north and northwest.  The initial intensity
is held at 30 kt based on earlier reports from the NOAA P3 and a
1254 UTC ASCAT-B scatterometer pass.

Karl remains located to the south and southwest of a mid-level
high.  However, the depression is expected to turn northwestward
later today when it begins to move between the high and a mid- to
upper-level low located near the Carolina coast.  Karl should then
turn northward and then accelerate toward the northeast from 48
hours and beyond once it becomes embedded in the mid-latitude
westerlies.  The track guidance remains in generally good agreement
on this scenario, and the main differences appear toward the end of
the forecast period when the ECMWF remains much slower than the
other models.  The new official forecast remains very close to a
consensus of the GFS and ECMWF models, which did not require any
significant changes from the previous advisory.

The distance between Karl and the upper-level low that has been
adversely affecting it during the past couple of days appears to be
increasing a bit, and the shear vector over the cyclone has become
south-southeasterly.  Although the global models continue to
indicate that the shear will decrease over the next few days, they
do not agree on the direction of that shear.  In addition, the
models do not agree on how much moisture there will be in the
mid-level environment around the cyclone.  As a result, the
intensity forecast is complicated, and confidence is not very high.
For continuity's sake, the updated intensity forecast is very
similar to the previous forecast during the first 3 days, and then
it is a little lower at days 4 and 5 based on the latest guidance.
Karl is expected to become extratropical by day 5, which agrees with
the latest guidance from the Ocean Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 20.8N  57.8W   30 KT  35 MPH
 12H  22/0000Z 22.1N  59.6W   30 KT  35 MPH
 24H  22/1200Z 24.0N  62.0W   30 KT  35 MPH
 36H  23/0000Z 25.7N  63.6W   35 KT  40 MPH
 48H  23/1200Z 27.2N  64.8W   45 KT  50 MPH
 72H  24/1200Z 31.0N  62.2W   60 KT  70 MPH
 96H  25/1200Z 36.0N  52.5W   70 KT  80 MPH
120H  26/1200Z 44.0N  38.5W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg/Gallina/Veenhuis
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