602
WTNT45 KNHC 200850
TCDAT5

Hurricane Teddy Discussion Number 32
NWS National Hurricane Center Miami FL AL202020
500 AM AST Sun Sep 20 2020

The convective structure of Teddy has degraded substantially since
the last advisory, with no sign of an eye in conventional satellite
imagery. The most recent available microwave imagery from last night
suggested that Teddy still had a very well defined low to mid-level
inner-core, but this has not translated to the higher levels more
apparent at night. Intensity estimates have decreased, so the
initial intensity has been lowered slightly to 100 kt for this
advisory. An Air Force Reserve Hurricane Hunter aircraft is
scheduled to investigate the hurricane later this morning and should
provide more information about its structure and strength.

Teddy's evolution for the next few days appears to be a tale of 3
troughs. Upper-level westerly flow associated with the first
upper-level trough, affecting the storm now, is the most likely
reason why the hurricane's structure has degraded and has taken on a
slightly sheared appearance. Teddy will begin to encounter the 2nd
trough, a deep frontal system approaching from the west, later today
and that should cause the hurricane to turn north. This interaction
should steer the center of Teddy east of Bermuda, but tropical storm
impacts from either the large hurricane, the frontal system, or both
are still likely Sunday evening through Monday night.

All indications are that Teddy will then continue generally
northward and merge with the frontal system, nearing Nova Scotia as
an extratropical cyclone early Wednesday. Teddy's maximum winds will
likely decrease sharply after it becomes post-tropical, as shown by
all the intensity guidance, but its gale and storm-force wind radii
will likely increase at the same time. The cyclone should turn
northeastward as the 3rd trough, another mid-latitude system,
approaches from the west. Teddy could be absorbed by that feature in
as soon as 120 h, though this is not explicitly shown in the
forecast at this time. The spread in the track and intensity
guidance is quite low and confidence in both aspects of the forecast
is high. There is a little more uncertainty in the wind radii
evolution, but it is clear that Teddy will produce strong winds over
a wide area of the northwest Atlantic during the next couple of
days.

The extent of 12-foot or higher seas associated with Teddy
continues to increase. See the Key Message below regarding swells
caused by the hurricane.


Key Messages:

1. The center of Teddy is forecast to move east of Bermuda late
Sunday or 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 early
next week, where there is an increasing risk of direct impacts from
wind, rain, and storm surge. Residents there should closely monitor
the progress of Teddy and updates to the forecast.

3. Large swells produced by Teddy are expected to affect portions
of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda,
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 20/0900Z 28.0N 62.0W 100 KT 115 MPH
12H 20/1800Z 28.9N 62.7W 95 KT 110 MPH
24H 21/0600Z 30.4N 62.9W 90 KT 105 MPH
36H 21/1800Z 33.3N 62.1W 85 KT 100 MPH
48H 22/0600Z 37.5N 62.2W 85 KT 100 MPH
60H 22/1800Z 40.9N 63.2W 75 KT 85 MPH...POST-TROP/EXTRATROP
72H 23/0600Z 43.8N 62.3W 60 KT 70 MPH...POST-TROP/EXTRATROP
96H 24/0600Z 51.0N 54.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 25/0600Z 58.5N 41.5W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Zelinsky
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