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Tropical Storm ODETTE

Tropical Storm Odette Discussion Number   1
NWS National Hurricane Center Miami FL       AL152021
500 PM EDT Fri Sep 17 2021
The circulation associated with the area of low pressure off the
U.S. Mid-Atlantic coast has become better defined today, with a
new center having developed near a persistent cluster of deep
convection.  This system has some non-tropical characteristics, with
a developing frontal boundary draped around the northern and western
side of the circulation.  Although the convection is being sheared
off to the northeast of the center, the structure still resembles
that of a tropical cyclone.  An ASCAT-C pass from a few hours ago
showed that maximum winds were 30-35 kt to the north of the center,
thus advisories are being initiated on Tropical Storm Odette with
35-kt winds.
With the re-formation of the center, the initial motion is
uncertain but is estimated to be northeastward, or 045/13 kt.
Odette is embedded between the subtropical ridge over the western
Atlantic and a deep-layer trough over the U.S. Upper Midwest and
central Canada.  The approach of this trough should cause Odette to
accelerate toward the northeast and then east-northeast during the
next few days.  After about day 3, there is significant divergence
among the models.  The GFS ejects the system northeastward and
stalls it over the north Atlantic, south of Greenland.  The ECMWF,
UKMET, and Canadian models, however, stall the cyclone sooner and
have it meandering south of Newfoundland on days 4 and 5.  For now,
the NHC track forecast shows Odette slowing down significantly on
those days (less than 5 kt on day 5) and is a blend of the TVCA and
HCCA consensus aids.
Odette's transition to an extratropical cyclone is probably already
underway.  The storm is also centered over the Gulf Stream, where 
water temperatures are about 28 degrees Celsius, so in the short 
term it is likely that a combination of baroclinic and convective 
forcing will cause some intensification, despite deep-layer shear 
strengthening to near 30 kt.  The global models suggest that Odette 
should become fully extratropical by 36 hours, and the intensity 
models indicate that the post-tropical low should peak in 
intensity in 48-60 hours.  The low is then likely to occlude by day 
3, a process which typically leads to gradual weakening, which is 
indicated in the official forecast.

Odette is expected to affect portions of Newfoundland with strong 
winds and heavy rainfall Sunday and Sunday night as a 
post-tropical cyclone.  Please refer to products from Environment 
Canada for additional information on potential impacts in 
INIT  17/2100Z 36.7N  71.8W   35 KT  40 MPH
 12H  18/0600Z 38.3N  69.3W   40 KT  45 MPH
 24H  18/1800Z 39.9N  65.9W   45 KT  50 MPH
 36H  19/0600Z 41.6N  61.7W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  19/1800Z 43.6N  57.1W   55 KT  65 MPH...POST-TROP/EXTRATROP
 60H  20/0600Z 45.0N  52.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  20/1800Z 46.0N  49.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  21/1800Z 47.0N  47.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  22/1800Z 47.5N  45.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
Forecaster Berg