[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 160850
TCDAT3

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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