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Post-Tropical Cyclone Teddy Forecast Discussion Number 43
2020-09-23 04:36:10| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 22 2020 000 WTNT45 KNHC 230236 TCDAT5 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. FORECAST POSITIONS AND MAX WINDS 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 48H 25/0000Z...ABSORBED BY A LARGER LOW $$ Forecaster Roberts
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