[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 240859
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  40
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 AM AST SAT SEP 24 2016

Data from an Air Force Reserve reconnaissance aircraft this morning
indicate that Karl has made the much anticipated turn toward the
northeast, and that the center has also reached its closest point of
approach to Bermuda. The strongest 825-mb flight-level wind measured
thus far has been 66 kt and the highest SFMR surface wind measured
has been 49 kt. The central pressure of 994 mb is based on a
recent dropsonde report. An earlier dropsonde report indicated that
the flight-level center was tilted to the northeast of the surface
center. Based on these data, the initial intensity is being
maintained at 55 kt.

The initial motion estimate is 035/15 kt. Karl is now coming under
the influence of deep southwesterly steering flow in advance of an
approaching strong mid-latitude trough and surface cold front. This
flow pattern should keep Karl moving northeastward away from Bermuda
and steadily increase its forward speed to 40-45 kt by 36-48 hours.
The new forecast track is similar to but slightly to the left of the
of the previous advisory track, and lies down the middle of the
tightly clustered track guidance.

Karl appears to have entrained some dry air in the mid- and low-
levels of the atmosphere based on reconnaissance data. However, the
cyclone is forecast to remain over SSTs of at least 27 deg C for the
next 24 hours or so within an environment of moderate vertical wind
shear.  This should allow Karl to strengthen to a hurricane in about
24-36 hours. After that, the cyclone is forecast to undergo
extratropical transition as it merges with the cold front, and this
should be complete by 48 hours, if not sooner.  The cyclone is
expected to be absorbed by a larger extratropical low between 48-72
hours.  The new intensity forecast is similar to the previous
advisory and lies close to the consensus model IVCN.



FORECAST POSITIONS AND MAX WINDS

INIT  24/0900Z 31.7N  64.3W   55 KT  65 MPH
 12H  24/1800Z 33.5N  61.2W   60 KT  70 MPH
 24H  25/0600Z 36.7N  54.9W   65 KT  75 MPH
 36H  25/1800Z 41.6N  45.6W   70 KT  80 MPH
 48H  26/0600Z 47.6N  36.4W   65 KT  75 MPH...POST-TROP/EXTRATROP
 72H  27/0600Z...DISSIPATED

$$
Forecaster Stewart
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