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Hurricane Lee Discussion Number  37
NWS National Hurricane Center Miami FL       AL132023
1100 AM AST Thu Sep 14 2023
 
The satellite presentation of Lee has degraded over the past day or 
so. An eye is no longer apparent but deep convection continues to 
wrap around the eastern and northern portions of the circulation. 
Deep convection has waned over the southwestern portions of the 
cyclone, likely due to an increase in southwesterly vertical wind 
shear and dry air entrainment. An Air Force Reserve reconnaissance 
aircraft that has been investigating Lee this morning has measured 
peak 700-mb flight-level winds of 96 kt, and the NOAA P-3 aircraft 
has found peak 8000 ft flight-level winds of 100 kt.  However, peak 
SFMR winds from both aircraft have been around 70 kt. Using a blend 
of the flight-level and SFMR data, the initial wind speed has been 
lowered to 80 kt, but this could be a little generous.
 
Lee is moving northward at a slightly faster forward speed of 12 kt. 
A faster northward to north-northeastward motion is expected during 
the next day or so around the western side of a mid-level ridge over 
the central Atlantic.  A slight bend to the north-northwest toward 
the Gulf of Maine is likely late Friday or early Saturday as the 
southern extent of mid-latitude trough moves off the Mid-Atlantic 
coast. After that time, Lee is forecast to turn northeastward over 
Atlantic Canada.  The dynamical model guidance is tightly clustered 
and only minor adjustments were made to the previous official 
forecast.  The NHC track is close to a blend of the typically 
reliable GFS and ECMWF models.
 
Southwesterly vertical wind shear is expected to increase over Lee 
during the next 24 to 36 hours, and this is likely to lead to 
gradual weakening during that time.  Sea surface temperatures will 
decrease significantly just after 36 hours when Lee moves north of 
the Gulf Stream.  The global model guidance suggests that Lee will 
begin extratropical transition Friday night and this is likely to be 
completed within 48 hours, if not a little sooner.  The NHC 
intensity forecast is a blend of the HFIP corrected consensus and 
and the IVCN consensus model.  It can't be stressed enough, that 
regardless of Lee's designation, it will remain a large and 
dangerous cyclone while it approaches eastern New England and 
Atlantic Canada.
 
 
KEY MESSAGES:
 
1. Tropical storm conditions, heavy rainfall, and high surf will
continue to impact Bermuda through Friday morning, and a Tropical
Storm Warning is in effect for the island.
 
2. Hurricane conditions and coastal flooding are possible in
portions of eastern Maine, southern New Brunswick, and western Nova
Scotia on Saturday, and a Hurricane Watch is in effect for that
area. Tropical storm conditions are expected on Cape Cod, Martha's
Vineyard, and Nantucket where a Tropical Storm Warning is now in
effect. Tropical storm conditions are possible elsewhere across New
England and Atlantic Canada within the Tropical Storm Watch areas.
 
3. Heavy rainfall from Lee may produce localized urban and small
stream flooding across eastern New England and into portions of New
Brunswick and Nova Scotia from Friday night into Saturday night.
 
4. There is the potential for life-threatening storm surge flooding 
in portions of southeastern Massachusetts, including Cape Cod and 
Nantucket, late Friday and Saturday, where a Storm Surge Watch is in 
effect.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  14/1500Z 30.4N  68.3W   80 KT  90 MPH
 12H  15/0000Z 32.2N  68.0W   75 KT  85 MPH
 24H  15/1200Z 35.0N  67.2W   70 KT  80 MPH
 36H  16/0000Z 38.2N  66.6W   70 KT  80 MPH
 48H  16/1200Z 41.5N  66.5W   65 KT  75 MPH
 60H  17/0000Z 44.0N  66.1W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  17/1200Z 47.0N  63.6W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  18/1200Z 52.6N  52.2W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  19/1200Z...DISSIPATED
 
$$
Forecaster Brown
 
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