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Hurricane Teddy Forecast Discussion


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000
WTNT45 KNHC 190851
TCDAT5

Hurricane Teddy Discussion Number  28
NWS National Hurricane Center Miami FL       AL202020
500 AM AST Sat Sep 19 2020

Teddy's satellite presentation has fluctuated through the early 
morning; most recently the eye has cooled and become poorly defined. 
GMI microwave imagery at 0350 UTC showed that Teddy was most of the 
way through an eyewall replacement cycle, and this is probably why 
its satellite appearance has degraded a little. AT 0600 UTC, a blend 
of objective and subjective intensity estimates still supported an 
intensity of 115 kt, but given recent trends noted in satellite 
imagery, the intensity is set at 110 kt for the advisory.

Little change was made to the NHC track or intensity forecasts, both 
of which remain near the model consensus throughout the forecast 
period. Teddy will likely turn northward by early Sunday as it 
approaches a frontal system over the western Atlantic. This should 
steer the hurricane east of Bermuda, though the hurricane's large 
wind field means that the island will still likely experience some 
tropical storm conditions begining Sunday afternoon or evening and 
continuing well into Monday. Fluctuations in intensity are likely 
through this period, but these fluctuations will have no impact on 
the overall size of Teddy's wind field, which is forecast to 
increase markedly, especially once it begins extratropical 
transition (ET).

The ET process could begin as soon as Monday, and based on GFS and 
ECMWF model fields, it should be complete in a little more than 72 
h. A rapid decrease in Teddy's max winds is expected after it 
becomes post-tropical, but the cyclone's wind field could actually 
expand further. The NHC forecast implies a due northward motion 
until the center of Teddy moves near Nova Scotia in about 4 days, 
but the cyclone's interaction with a cut-off low and a building 
ridge to the east of the cyclone could deflect it a little to the 
left between 72 and 96 h. A turn toward the northeast is expected by 
the end of the forecast as Teddy interacts with another mid-latitude 
trough approaching from the northwest.

Teddy an extensive area of large waves and swells which are 
impacting much of the western Atlantic basin.  See the Key Messages 
below.


Key Messages:

1. While the center of Teddy is forecast to move east of Bermuda
late Sunday or Monday, Tropical Storm conditions are still likely 
for the island and its nearby waters beginning Sunday afternoon or 
evening. A Tropical Storm Warning is in effect.

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 through the
weekend.

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  19/0900Z 24.9N  58.2W  110 KT 125 MPH
 12H  19/1800Z 26.3N  59.5W  110 KT 125 MPH
 24H  20/0600Z 28.0N  61.2W  105 KT 120 MPH
 36H  20/1800Z 29.5N  62.2W  100 KT 115 MPH
 48H  21/0600Z 31.6N  61.9W   95 KT 110 MPH
 60H  21/1800Z 35.2N  61.1W   95 KT 110 MPH
 72H  22/0600Z 39.2N  61.3W   90 KT 105 MPH
 96H  23/0600Z 45.5N  61.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  24/0600Z 51.5N  53.5W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Zelinsky