000
WTNT42 KNHC 210238
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 PM AST TUE SEP 20 2016

Karl continues to struggle this evening.  Satellite images indicate
that the low-level center of the storm is completely exposed to the
southwest of the main area of deep convection.  The NOAA Hurricane
Hunters investigated Karl earlier this evening and found that the
maximum winds were still around 35 kt, though a very recent ASCAT
pass suggests that this estimate could be a bit generous.

Dropsonde data and model vertical cross sections indicate that Karl
is being affected by mid-level southwesterly flow and dry air
induced by a cut-off low pressure system located a few hundred
miles to the west.  These unfavorable atmospheric conditions have
been affecting the cyclone during the past several days and until
these conditions abate, little change in the structure or strength
of Karl is anticipated.  The models insist that environment should
become less hostile in about 24 h, and Karl should have its best
opportunity to intensify late this week and this weekend when it
moves into an area of baroclinic forcing.  The NHC intensity
forecast is identical to the previous one, and lies near the middle
of the guidance envelope.

The tropical storm has moved basically due west during the past 24
hours.  A turn toward the northwest should occur on Wednesday
when the cyclone nears the southwestern periphery of a deep-layer
ridge, followed by a northward motion in about 3 days when Karl
rounds the ridge and moves into a pronounced weakness.  By the end
of the forecast period, a sharp increase in speed and turn to the
northeast are expected as a large-scale mid-latitude trough
picks up the tropical cyclone. There are significant forward speed
differences in the models associated with how Karl interacts with
the large-scale trough in the 3 to 5 day time frame, and the
NHC forecast is of low confidence during that period.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0300Z 19.9N  56.7W   35 KT  40 MPH
 12H  21/1200Z 20.9N  58.2W   35 KT  40 MPH
 24H  22/0000Z 22.9N  60.7W   40 KT  45 MPH
 36H  22/1200Z 24.5N  62.9W   45 KT  50 MPH
 48H  23/0000Z 25.9N  64.8W   55 KT  65 MPH
 72H  24/0000Z 29.0N  65.0W   70 KT  80 MPH
 96H  25/0000Z 32.9N  59.6W   85 KT 100 MPH
120H  26/0000Z 39.2N  48.2W   80 KT  90 MPH

$$
Forecaster Cangialosi