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Hurricane Lee Discussion Number  30
NWS National Hurricane Center Miami FL       AL132023
Issued by the NWS Weather Prediction Center College Park MD
500 PM AST Tue Sep 12 2023
 
GOES-East satellite and information from an Air Force Reserve 
Hurricane Hunter plane indicate a slight recent improvement in the 
inner-eye structure with a 5-mb pressure fall noted in the most 
recent pass.  However, peak 700-mb flight-level winds were lower 
than 6 hr ago with SFMR estimates about the same.   Given the mixed 
signals, we will maintain the initial wind speed at 100 kts for 
this advisory.   The big change in the aircraft data was the sizable
expansion of the whole wind field in the eastern semicircle 
of the hurricane, which was also shown by a late-arriving SAR pass 
this morning.

Lee has turned northwestward (315/6 kt) as the mid-level ridging 
continues to its north and east.  A digging eastern United States 
trough remains on track to weaken the ridge during the next few 
days.  Lee is expected to turn more northward and accelerate by 
Thursday as a result of this pattern change.  Even though the core 
of Lee is expected to be well west of Bermuda, Lee's large wind 
field could arrive early Thursday on the island.  After day 3, 
there is an increase in guidance spread as the hurricane interacts 
with an approaching frontal zone, which could cause a small 
leftward bend in the track.  However, recent guidance has tightened 
somewhat, and the official forecast follows a middle-ground 
solution similar to the GEFS/ECMWF ensemble means, on the fast side 
of the consensus. 

The hurricane is expected to gradually weaken over the next few 
days while it moves over cooler waters into a higher-shear 
environment.  Still, all of the guidance keep this system quite 
large and at hurricane-strength for the next few days.  Once the 
circulation reaches the colder water north of the Gulf Stream, more 
significant weakening is expected at the day 4-5 period as it 
quickly transitions to an extratropical low.  Little change was 
made to the previous forecast, which is also close to the consensus 
aids, and the forward speed north of the Gulf Stream will be 
important in the exact wind speed as Lee approaches the mainland.

Note- The 34- and 50-kt wind speed probabilities beyond 36 hours in 
the text product and graphics 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. There is an increasing risk of strong winds, rainfall, and high
surf impacts to Bermuda later this week, and a Tropical Storm Watch
remains in effect for the island.
 
3. It remains too soon to know what level of additional impacts Lee
might have along the northeastern U.S. coast and Atlantic Canada
late this week and this weekend.  However, since wind and rainfall
hazards will extend well away from the center as Lee grows in size,
users should continue to monitor updates to Lee's forecast during
the next several days.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/2100Z 24.7N  66.4W  100 KT 115 MPH
 12H  13/0600Z 25.4N  67.0W  100 KT 115 MPH
 24H  13/1800Z 26.7N  67.6W   95 KT 110 MPH
 36H  14/0600Z 28.6N  68.1W   90 KT 105 MPH
 48H  14/1800Z 30.7N  68.2W   85 KT 100 MPH
 60H  15/0600Z 33.4N  67.6W   80 KT  90 MPH
 72H  15/1800Z 36.4N  66.8W   75 KT  85 MPH
 96H  16/1800Z 42.8N  66.5W   65 KT  75 MPH
120H  17/1800Z 47.1N  64.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Gallina/Blake/Bann
 
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