[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 212050
TCDAT5

Hurricane Teddy Discussion Number  38
NWS National Hurricane Center Miami FL       AL202020
500 PM AST Mon Sep 21 2020

Teddy is gradually losing tropical characteristics with weaker deep
convection near the center and more convective asymmetry. The
initial wind speed is kept at 80 kt, assuming any decrease in
organization has been offset by the doubling of the forward speed
since the last advisory. Note that Dvorak estimates are likely to
underestimate the true maximum winds in this extratropical
transition situation.

The hurricane is now moving quickly northward as a mid-latitude
trough picks up the cyclone. All of the guidance show Teddy
strengthening overnight due to a baroclinic energy infusion from
this trough and increased instability from the warmer waters of the
Gulf Stream/North Atlantic.  Afterward, Teddy should lose its
baroclinic forcing and move over cooler water late Tuesday, causing
weakening while it accelerates to the north-northeast across
eastern Nova Scotia, the Gulf of St. Lawrence and Newfoundland
before dissipating in 3-4 days. No significant changes were made to
the track forecast except for a westward shift beyond 48 hours.
While there is some uncertainty about the exact status of Teddy near
Nova Scotia, since much of the model guidance keeps the cyclone
with a warm core and some convection, it doesn't change the hazards
much with significant chances of high winds, heavy rain, storm
surge and destructive waves for the south coast of Nova Scotia.

Teddy's size will likely double during the next couple of days as
it moves northward and interacts with the aforementioned trough.
Gale-force winds are likely along portions of the near shore waters
of the northeast United States. Please see products from your local
office for more information about marine hazards, including
extremely dangerous rip currents expected over much of the western
Atlantic beaches.

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 Tuesday through Thursday, where direct impacts from wind, rain,
and storm surge are expected. Tropical Storm Watches and Warnings
are in effect for portions of Nova Scotia, Prince Edward Island and
Newfoundland.

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. Heavy rainfall across Atlantic Canada is expected with Teddy
between Tuesday and Thursday after it becomes a strong post-tropical
cyclone.

FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 33.2N  62.0W   80 KT  90 MPH
 12H  22/0600Z 36.5N  62.5W   90 KT 105 MPH
 24H  22/1800Z 39.5N  63.7W   80 KT  90 MPH
 36H  23/0600Z 42.2N  63.2W   70 KT  80 MPH
 48H  23/1800Z 46.5N  61.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
 60H  24/0600Z 50.5N  58.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  24/1800Z 54.5N  53.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  25/1800Z...DISSIPATED

$$
Forecaster Blake
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