Hurricane Teddy Discussion Number  26
NWS National Hurricane Center Miami FL       AL202020
500 PM AST Fri Sep 18 2020

Both NOAA and U.S. Air Force Hurricane Hunter aircraft have been 
investigating Teddy since this morning. The highest flight level 
wind measured by the aircraft was 119 kt at 750 mb, which reduces to 
around 101 kt at the surface. The latest central measured by the 
aircraft is up 4 mb from the previous advisory, indicating only some 
slight weakening. Earlier microwave images indicated that an eyewall 
replacement cycle had been taking place and some drier air had 
intruded into the southern portion of the circulation, leaving a 
partial break in the eyewall. This may explain the reason why the 
aircraft have not been finding winds as strong as they did 
previously, and in fact found a double wind maxima in the northern 
portion of the circulation. These eyewall replacement cycles are 
common in intense tropical cyclones, and oftentimes the systems 
recover within 12-24 h as long as the environmental conditions 
support it. Over the past hour or so, the ring of deep convection 
has appeared less broken and is beginning to expand in size, which 
could be an indication that the hurricane is recovering from the 
eyewall replacement. Based on the possibility of some undersampling 
by the aircraft, the increase of only 4 mb in central pressure, and 
the latest convective trends, the initial intensity is being lowered 
only slightly to 110 kt. 

Teddy continues its long trek northwestward, now at 12 kt. The 
hurricane is expected to remain on that general course during the 
next couple of days as it moves on the southwestern periphery of a 
mid-level ridge.  By the end of the weekend, when Teddy will likely 
be approaching Bermuda, a turn to the north or north-northeast is 
forecast to occur as a mid- to upper-level trough moves off the 
northeastern U.S. coast. Early next week, the trough is expected to 
cut off, causing Teddy to turn slightly to the left and approach 
Nova Scotia in about 4 days.  The models continue to be in good 
agreement on this scenario, and only small adjustments were made to 
the previous forecast track.

The environment around Teddy will be conducive for maintaining an 
intense hurricane for the next 24 h or so, as the ocean 
temperatures will remain warm with low vertical wind shear and a 
fairly moist atmosphere. After 24 h, the hurricane is forecast to 
cross cooler waters churned up by Paulette last week. This should 
cause a slow weakening trend to begin. By Monday night, vertical 
wind shear is expected to drastically increase ahead of an 
approaching mid-latitude trough. This should not only weaken 
Teddy, but begin its transition to a large extratropical cyclone, 
and that transition should be completed around day 4 of the forecast 
period. The latest NHC intensity forecast is near or a little above 
HCCA and IVCN through 24 h, and then trends toward the SHIPS 
intensity guidance thereafter. 

Teddy is producing a large area of high seas.  The latest maximum
seas estimated by TAFB near the core of the hurricane are near 45
feet.  Swells from Teddy are spreading far from the center, see Key
Messages below.

Key Messages:

1. While the center of Teddy is forecast to move east of Bermuda 
late Sunday or Monday, there is still a risk of strong winds, storm 
surge, and heavy rainfall on the island, and a Tropical Storm Watch 
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  18/2100Z 23.1N  57.0W  110 KT 125 MPH
12H  19/0600Z 24.5N  58.1W  110 KT 125 MPH
24H  19/1800Z 26.5N  59.9W  110 KT 125 MPH
36H  20/0600Z 28.1N  61.6W  105 KT 120 MPH
48H  20/1800Z 29.7N  62.6W  100 KT 115 MPH
60H  21/0600Z 31.8N  62.5W   95 KT 110 MPH
72H  21/1800Z 35.6N  61.7W   85 KT 100 MPH
96H  22/1800Z 43.2N  62.7W   75 KT  85 MPH...POST-TROP/EXTRATROP
120H  23/1800Z 48.5N  59.3W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Latto