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Tropical Storm Odette Discussion Number   3
NWS National Hurricane Center Miami FL       AL152021
500 AM AST Sat Sep 18 2021
 
Odette does not look very much like a tropical cyclone.  All of the 
deep convection continues to be displaced well to the east of the 
poorly-defined center due to strong westerly shear.  The circulation 
is elongated from southwest to northeast and contains multiple 
low-cloud swirls.  The current intensity of the system is estimated 
to be near 40 kt based on earlier scatterometer observations, and 
these stronger winds are occurring in the convection over the 
eastern semicircle of the cyclone, well removed from the center.

Since the center is not so easy to locate, the motion is rather 
uncertain.  However the system appears to be accelerating and the 
initial motion estimate is roughly 050/13 kt.  Odette is embedded 
within the flow on the south side of a mid-latitude shortwave 
trough.  This steering pattern should carry the system northeastward 
to east-northeastward for the next couple of days.  Afterwards, the 
trough is predicted by the global models to cut off to the south of 
eastern Newfoundland.  As a result, Odette is likely to turn a 
little south of east and decelerate in 3-4 days.  By the end of the 
forecast period, the cyclone is expected to begin moving 
northeastward on the east side of the cutoff low.  The official 
track forecast is similar to the previous one but a little farther 
south around days 4 and 5.  This is in good agreement with the 
latest corrected model consensus.

The dynamical guidance indicates that the vertical shear over 
Odette will get even stronger over the next few days.   As the 
system will soon begin to move over the cooler waters to the north 
of the Gulf Stream, its primary energy source should come from 
baroclinicity.  In about 24 hours, the dynamical guidance shows 
significant thermal advection around the cyclone, signifying its 
extratropical transition.  The global models show the post-tropical 
cyclone deepening through 48 hours and the official forecast calls 
for some strengthening up to that time.  Later in the period, as 
the baroclinic energy source appears to wane, gradual weakening is 
expected.
 
As Odette becomes fully extratropical and gains latitude this
weekend and into Monday, the wind field is forecast to expand 
significantly.  Odette is expected to affect portions of 
Newfoundland with strong winds and heavy rainfall Sunday and Monday 
as a strong post-tropical cyclone.  Please refer to products 
from Environment Canada for additional information on potential 
impacts in Newfoundland.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0900Z 38.0N  69.3W   40 KT  45 MPH
 12H  18/1800Z 39.2N  66.7W   45 KT  50 MPH
 24H  19/0600Z 40.8N  62.7W   50 KT  60 MPH...POST-TROP/EXTRATROP
 36H  19/1800Z 42.4N  58.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 48H  20/0600Z 43.3N  54.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 60H  20/1800Z 43.5N  51.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  21/0600Z 43.0N  48.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  22/0600Z 42.5N  46.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  23/0600Z 43.0N  46.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Pasch
 
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