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Hurricane Lee Discussion Number  32
NWS National Hurricane Center Miami FL       AL132023
500 AM AST Wed Sep 13 2023
 
Lee's structure is very gradually declining in organization.  The 
hurricane has a ragged but somewhat elliptical 25-30 n mi wide eye, 
but deep convection has become eroded a bit within the western 
semicircle, possibly due to some moderate westerly shear.  In 
addition, a 0607 UTC AMSR-2 microwave pass showed that the eyewall 
was open on the southwest side at that time.  Subjective and 
objective satellite estimates range from 90-105 kt, so Lee's 
initial intensity remains 100 kt for now.

The hurricane is very slowly making its turn around a west-central 
Atlantic mid-level high, with its motion now northwestward at 
325/5 kt.  The track guidance is tightly clustered during the next 
2 days or so, showing Lee turning and accelerating toward the 
north-northwest and north between the high and a shortwave trough 
swinging across the Great Lakes region.  Lee's core is forecast to 
pass west of Bermuda in 36-48 hours, but tropical storm conditions 
are likely to begin there late tonight or early Thursday due to the 
hurricane's large wind field.  On days 3 and 4, Lee is expected to 
maintain a general northward track offshore the northeastern U.S. 
However, the global models are suggesting that the hurricane 
will interact with a remnant mid-level trough over the mid-Atlantic 
states, causing Lee to possibly bend just west of due north while 
it moves across the Gulf of Maine.  Under the assumption that the 
global models will have a better handle on this mid-latitude 
pattern as compared to the regional hurricane models, the NHC track 
forecast is close to a consensus of the GFS and ECMWF models (GFEX) 
on days 3, 4, and 5, and therefore ends up being a bit west and 
then north of the previous prediction on those days.
 
A number of factors--including Lee's broad structure, increasing 
shear, and potential upwelling of cooler waters--are likely to lead 
to a very gradual decrease in the hurricane's maximum winds during 
the next 3 days or so.  In addition, Lee is likely to begin 
extratropical transition in 2-3 days, with that process expected to 
be complete just before the cyclone's center reaches the coast of 
Maine, New Brunswick, or Nova Scotia in about 4 days.  That said, 
Lee's expected post-tropical transition will not diminish potential 
wind, rain, and coastal flooding impacts in New England and Atlantic 
Canada due to the system's broad wind field. 
 
It should again be noted that the 34- and 50-kt wind speed
probabilities beyond 36 hours in the text and graphical products are
likely underestimating the risk of those winds occurring.  This is
because the forecast wind field of Lee is considerably larger than
average compared to the wind field used to derive the wind speed
probability product.
 
 
KEY MESSAGES:
 
1. Dangerous surf and life-threatening rip currents will affect
portions of the northern Leeward Islands, the Virgin Islands, Puerto
Rico, Hispaniola, the Turks and Caicos Islands, the Bahamas,
Bermuda, and most of the U.S East Coast through much of the week.
 
2. Tropical storm conditions, heavy rainfall, and high surf are
expected to impact Bermuda beginning late tonight or early Thursday, 
and a Tropical Storm Warning is in effect for the island.
 
3. There is an increasing risk of wind, coastal flooding, and rain 
impacts from Lee in portions of New England and Atlantic Canada 
beginning on Friday and continuing through the weekend.  Watches may 
be required for portions of these areas later today or tonight.  
Due to Lee's large size, hazards will extend well away from the 
center, and there will be little to no significance on exactly where 
the center reaches the coast. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0900Z 25.7N  67.1W  100 KT 115 MPH
 12H  13/1800Z 26.6N  67.6W   95 KT 110 MPH
 24H  14/0600Z 28.4N  68.1W   90 KT 105 MPH
 36H  14/1800Z 30.5N  68.3W   85 KT 100 MPH
 48H  15/0600Z 33.0N  68.0W   80 KT  90 MPH
 60H  15/1800Z 36.1N  67.4W   75 KT  85 MPH
 72H  16/0600Z 39.6N  67.3W   70 KT  80 MPH
 96H  17/0600Z 45.2N  67.3W   50 KT  60 MPH...POST-TROP/INLAND
120H  18/0600Z 51.0N  61.4W   35 KT  40 MPH...POST-TROP/INLAND
 
$$
Forecaster Berg
 
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