[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 231445
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  37
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM AST FRI SEP 23 2016

A NOAA P3 flight continued to fly through Karl for a few hours
after the release of the last advisory, and while it didn't find
winds higher than 50 kt, dropsonde data did indicate that the
minimum pressure had fallen to 992 mb.  Microwave data indicate
that Karl is still under the influence of 15-20 kt of south-
southeasterly shear.  The convective pattern has continued to
improve, however, with an elongated curved band extending to the
northeast and east of the central convection.

With sea surface temperatures running between 29-30C for the next
24 hours and vertical shear expected to decrease slightly, it seems
likely that Karl will continue to strengthen during the next couple
of days.  The intensity guidance is in fairly good agreement on the
intensification trend, and in fact most of the models are showing
Karl reaching a strength between 60 and 65 kt in about 24 hours.
Therefore, the updated official forecast now shows Karl reaching
hurricane intensity at that time.  Continued strengthening is
likely after that time, and the peak intensity shown in the
official forecast is slightly higher than the previous forecast at
48 hours, which is in line with the latest guidance.  Karl will be
in the process of extratropical transition at that time, but the
global models fields only agree that the transition will be
complete by 72 hours.  Karl should then be absorbed by a larger
extratropical low by day 4.

The last fix from the NOAA P3 was a little east of the previous Air
Force fixes, so it's possible that Karl's center has begun to move
east of due north.  Until we know for sure, the initial motion is
set to be northward, or 360/10 kt.  Karl is located near the
western edge of the subtropical ridge axis, and it should become
increasingly embedded in the mid-latitude westerlies during the next
couple of days. Therefore, the cyclone is forecast to turn
northeastward and begin accelerating within the next 24 hours, with
the motion becoming even faster by 72 hours. The spread among the
track models is extremely tight on this forecast cycle, and very
little change was required from the previous advisory.  The new
official forecast lies very close to the TVCN multi-model consensus.

Since Karl is now forecast to become a hurricane by 24 hours while
the center is passing just to the east of Bermuda, the Bermuda
Weather Service has elected to issue a Hurricane Watch for the
island.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 28.6N  64.8W   50 KT  60 MPH
 12H  24/0000Z 30.2N  64.8W   55 KT  65 MPH
 24H  24/1200Z 32.3N  62.7W   65 KT  75 MPH
 36H  25/0000Z 34.9N  57.8W   70 KT  80 MPH
 48H  25/1200Z 38.9N  49.8W   75 KT  85 MPH
 72H  26/1200Z 50.7N  29.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
 96H  27/1200Z...ABSORBED BY A LARGER EXTRATROPICAL LOW

$$
Forecaster Berg/Sullivan/Gerhardt/Schichtel
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