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Post-Tropical Cyclone Odette Forecast Discussion


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000
WTNT45 KNHC 182034
TCDAT5

Post-Tropical Cyclone Odette Discussion Number   5
NWS National Hurricane Center Miami FL       AL152021
500 PM AST Sat Sep 18 2021

Odette appears to have completed extratropical transition, perhaps 
a little earlier than the global models want to admit.  The cyclone 
has developed a frontal structure similar to that of a bent back 
occlusion, with cold-air stratocumulus clouds advecting eastward 
to the south of the center behind the trailing cold front.  In 
addition, the remaining deep convection is closer to the system's 
triple point than multiple-swirled center of circulation.  The 
initial intensity is highly uncertain since all three ASCAT 
instruments completely missed the area where the strongest winds 
were likely to have been occurring, and it is held at 40 kt based on 
continuity.

The post-tropical cyclone has turned to the east-northeast and is 
moving a little faster--now with a motion of 060/16 kt.  Additional 
acceleration is expected during the next 24 hours while Odette is 
embedded in the mid-latitude westerlies.  After 24 hours, Odette is 
expected to detach from the prevailing flow, which will cause the 
cyclone to slow down and meander southeast of Newfoundland by days 
3 through 5.  The track guidance has shifted slightly southward on 
this cycle, and the NHC forecast follows that trend and continues 
to hedge toward a consensus of the GFS and ECMWF models.

Now that Odette is extratropical, global models indicate that 
baroclinic forcing should support strengthening and expanding of 
the gale-force wind field during the next couple of days.  During 
this evolution, the strongest winds will also migrate to the 
northern and western side of the circulation.  The frontal low is 
expected to occlude in about 3 days, coincident with the beginning 
of its meandering motion, and that occlusion process should cause a 
slow weakening of the winds through the end of the forecast period. 
One caveat is that some of the models have been hinting that the 
occluded low could redevelop deep convection near the center and 
transition to a tropical or subtropical cyclone, but there has not 
been enough consistency among the guidance to explicitly make that 
forecast.  If the system's forecast track continues to shift 
southward toward warmer waters on days 3 through 5, that scenario 
could become a stronger possibility.

Post-Tropical Cyclone Odette is forecast to affect portions
of Newfoundland with strong winds and heavy rainfall Sunday and
Monday.  Please refer to products from the Canadian Hurricane
Centre for additional information on potential impacts in
Newfoundland.

This is the last advisory issued by the National Hurricane Center 
on Odette.  Additional information on this system can be found in 
High Seas Forecasts issued by the National Weather Service, under 
AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at 
ocean.weather.gov/shtml/NFDHSFAT1.php


FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 39.1N  65.1W   40 KT  45 MPH...POST-TROP/EXTRATROP
 12H  19/0600Z 40.5N  62.1W   45 KT  50 MPH...POST-TROP/EXTRATROP
 24H  19/1800Z 41.9N  58.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 36H  20/0600Z 42.3N  54.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 48H  20/1800Z 41.8N  51.3W   50 KT  60 MPH...POST-TROP/EXTRATROP
 60H  21/0600Z 40.7N  48.9W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  21/1800Z 40.0N  47.2W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  22/1800Z 41.4N  47.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  23/1800Z 43.2N  48.8W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg