542
WTNT45 KNHC 202056
TCDAT5

Hurricane Teddy Discussion Number 34
NWS National Hurricane Center Miami FL AL202020
500 PM AST Sun Sep 20 2020

Satellite images show that Teddy is continuing to maintain a
central core, albeit eroded on the western side due to shear and
dry air. However, the latest microwave data show a more distinct
eye than conventional data would indicate, along with an open
eyewall. The initial intensity is held at 90 kt, pending Air
Force Reserve Hurricane Hunter aircraft data this evening.

The hurricane has turned north-northwestward and is likely to
turn northward tonight and north-northeastward tomorrow due to an
approaching large mid-latitude trough. By early Tuesday, the
cyclone should turn back to the north-northwest as it rotates
around the same trough, then turn northeastward early Wednesday
ahead of yet another trough moving into from eastern Canada.
Track model guidance remains in very good agreement, and only a
slight westward adjustment was made to the forecast.

The global models are in excellent agreement on Teddy transitioning
into a large non-tropical low between Bermuda and Nova Scotia in
about 2 days. In many respects, the upcoming trough interaction
reminds me of an extratropical transition like Sandy 2012,
thankfully happening at a good distance from land, with the
GFS/ECMWF models showing pressures into the 940s tomorrow, a slight
increase in maximum winds, and a large increase in the size of the tropical-storm-force winds. Beyond Tuesday, the hurricane should
become post-tropical near or south of Nova Scotia and be absorbed by
a larger extratropical low after day 4 to the northeast of
Newfoundland. Little change was made to the official forecast,
other than show a small increase tomorrow as the peak extratropical
forcing deepens the cyclone. It is still worth noting every model
has a rather large and strong post-tropical cyclone near Nova Scotia
in 2-3 days, with hazards that will extend a very long way from the
center.

Extremely dangerous surf conditions with 20-ft waves have been
reported on the south shore of Bermuda, and officials are
encouraging residents to avoid going into or near the water.

Key Messages:

1. The center of Teddy is forecast to move east of Bermuda on
Monday. Tropical storm conditions are likely on the island beginning
this evening and could continue into Monday evening.

2. Teddy is expected to transition to a powerful post-tropical
cyclone as it moves near or over portions of Atlantic Canada
late Tuesday through Thursday, where there is an increasing risk of
direct impacts from wind, rain, and storm surge. A Tropical Storm
Watch has been issued for portions of Nova Scotia, and heavy rain is
also expected across sections of Atlantic Canada.

3. 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 could cause life-threatening surf and rip
current conditions.


FORECAST POSITIONS AND MAX WINDS

INIT 20/2100Z 29.0N 63.4W 90 KT 105 MPH
12H 21/0600Z 30.1N 63.5W 85 KT 100 MPH
24H 21/1800Z 32.8N 62.6W 90 KT 105 MPH
36H 22/0600Z 36.9N 63.0W 90 KT 105 MPH
48H 22/1800Z 40.0N 64.0W 85 KT 100 MPH
60H 23/0600Z 42.7N 63.5W 75 KT 85 MPH...POST-TROP/INLAND
72H 23/1800Z 46.0N 61.3W 60 KT 70 MPH...POST-TROP/EXTRATROP
96H 24/1800Z 54.5N 50.5W 40 KT 45 MPH...POST-TROP/EXTRATROP
120H 25/1800Z...DISSIPATED

$$
Forecaster Blake
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