[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 122057
TCDAT3

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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