[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 180836
TCDAT5

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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