Official Discussion issued by the National Hurricane Center

(AL202020) DATA RELEASED: 9/23/2020 3:00:00 AM UTC

Copy of official data

Post-Tropical Cyclone Teddy Discussion Number  43
NWS National Hurricane Center Miami FL       AL202020
1100 PM AST Tue Sep 22 2020

Extratropical transition has been ongoing since last night, with
the cyclone's associated rain shield expanding over a great 
distance in the northern semicircle.  In addition, multiple
dropsonde observations from the Air Force Reserve hurricane hunters
and buoy data show a sharp temperature gradient of nearly 20
degrees F from northwest quadrant to the southeast, indicative of
the cyclone's involvement with the strong baroclinic frontal zone.
Accordingly, Teddy has become a strong post-tropical extratropical
cyclone.  Highest flight-level winds recorded this evening were 83
kt about 85 miles northeast of the center and the highest SFMR
surface winds were 63 kt.  A recent METOP-C scatterometer pass 
showed sustained winds no higher than 59 kt in the east quadrant.
A blend of these data yields an initial intensity of 70 kt for this 
advisory.  Further gradual weakening is forecast through the period 
as a result of the rapidly decreasing sea surface temperatures 
(less than 20C) north of the North Wall of the gulf stream.  The 
NHC forecast indicates Teddy approaching the coast of Nova Scotia 
below hurricane strength, but still as a strong post-tropical 
extratropical low.  Teddy should continue to gradually spin down as 
the cyclone moves north-northeastward toward Newfoundland.

The initial motion is estimated to be northward, or 010/16 kt.
A north-northeastward turn is forecast later tonight or early 
Wednesday in response to an approaching mid-latitude shortwave 
trough moving out of the northeast U.S.  Teddy should move over 
Nova Scotia tomorrow and near the island of Newfoundland, and the 
adjacent waters of the Gulf of St. Lawrence Wednesday night.  
Afterward, the post-tropical cyclone will likely be absorbed by an 
even larger high latitude extratropical cyclone near Greenland.  
There has been no significant changes made to the NHC forecast 
track this evening, and it's in best agreement with the HFIP 
Corrected Consensus Approach model.

Key Messages:

1. Teddy is expected to transition to a powerful post-tropical
cyclone as it moves near or over portions of Atlantic Canada
late today through Thursday. The most significant hazard expected
from Teddy is large destructive waves forecast along the southern
coast of Nova Scotia through Wednesday.

2. Very large swells produced by Teddy are expected to affect
portions of Bermuda, the Leeward Islands, the Greater Antilles, the
Bahamas, the east coast of the United States, and Atlantic Canada
during the next few days. These swells are expected to cause
life-threatening surf and rip current conditions.

3. Tropical Storm Watches and Warnings are in effect for portions
of Nova Scotia, Newfoundland, Prince Edward Island and the Magdalen
Islands, and heavy rainfall across Atlantic Canada is expected
through Thursday.


INIT  23/0300Z 42.8N  63.9W   70 KT  80 MPH...POST-TROPICAL
12H  23/1200Z 45.3N  62.3W   60 KT  70 MPH...INLAND
24H  24/0000Z 49.8N  58.7W   50 KT  60 MPH...POST-TROP/EXTRATROP
36H  24/1200Z 54.7N  54.9W   45 KT  50 MPH...POST-TROP/EXTRATROP

Forecaster Roberts