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Post-Tropical Cyclone Lee Discussion Number  44
NWS National Hurricane Center Miami FL       AL132023
500 AM AST Sat Sep 16 2023
 
Lee appears to have completed its transition to a post-tropical 
cyclone.  The cloud pattern is comma shaped, and there has been no 
significant central deep convection for the past 12 hours or so.  
The cyclone is now frontal but likely still has a warm core, 
indicating that it is a warm seclusion-type of extratropical 
cyclone.  Despite this transition, it remains a potent cyclone, and 
the initial intensity remains 70 kt since the Air Force Reserve 
Hurricane Hunters measured SFMR winds as high as 66 kt about 110 n 
mi southwest of the center.

Lee accelerated more than expected during the past 6-12 hours, and 
the current motion is estimated to be northward (355 degrees) at 22 
kt.  The aircraft fixes and recent satellite imagery indicate that 
the center has bent back to the west by just a bit, which was 
expected, likely due to interaction with a mid-level trough which 
moved off the U.S. Mid-Atlantic coast.  A general northward motion, 
but at a slower forward speed, is expected today, and Lee's center 
is now forecast to reach western Nova Scotia around midday.  The 
cyclone is then expected to turn toward the north-northeast and 
then northeast, moving across Atlantic Canada and the Gulf of St. 
Lawrence tonight through Sunday.  Due to the recent acceleration, 
the new NHC track forecast is faster than, but still otherwise on 
top of, the previous prediction. 
 
Lee's center has moved north of the Gulf Stream, and water 
temperatures along the cyclone's path are down to 20 degrees 
Celsius and decreasing.  Intensity models indicate that Lee should 
begin gradually weakening very soon, although the maximum winds are 
likely to still be at or just below hurricane strength (mainly 
over water) when Lee's center reaches Nova Scotia later today.  The 
NHC intensity forecast closely follows the GFS and ECMWF solutions, 
and Lee is expected to continue producing gale-force winds while it 
moves across Atlantic Canada tonight through Sunday.

 
KEY MESSAGES:
 
1. Hurricane conditions are possible across portions southern New
Brunswick and Nova Scotia later today within the Hurricane Watch 
areas.  Tropical storm conditions and coastal flooding are
occurring across portions of coastal New England and Atlantic 
Canada, and will continue to spread northward within the Tropical 
Storm Warning areas.  The strong winds are likely to lead to downed 
trees and potential power outages.
 
2. Heavy rainfall from Lee may produce localized urban and small 
stream flooding in portions of far eastern Massachusetts, eastern 
Maine, New Brunswick, and western Nova Scotia today.

3. Dangerous surf and life-threatening rip currents will continue 
to affect the U.S. East Coast, Atlantic Canada, Bermuda, the 
Bahamas, the Turks and Caicos Islands, Hispaniola, Puerto Rico, the 
Virgin Islands, and the northern Leeward Islands through the 
weekend.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/0900Z 41.8N  66.0W   70 KT  80 MPH...POST-TROP/EXTRATROP
 12H  16/1800Z 44.1N  65.6W   55 KT  65 MPH...POST-TROP/EXTRATROP
 24H  17/0600Z 46.8N  64.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 36H  17/1800Z 49.5N  60.1W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  18/0600Z 52.3N  53.4W   40 KT  45 MPH...POST-TROP/EXTRATROP
 60H  18/1800Z...ABSORBED BY ANOTHER LOW
 
$$
Forecaster Berg
 
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