[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 120851
TCDAT3

Hurricane Lee Discussion Number  28
NWS National Hurricane Center Miami FL       AL132023
500 AM AST Tue Sep 12 2023

Lee continues to exhibit a concentric eyewall structure in
conventional satellite imagery. This has been confirmed by the Air
Force Reserve Hurricane Hunters that investigated Lee early this
morning, and they reported the outer eyewall had a large diameter of
80 n mi. The maximum 700-mb flight-level wind measured by the
aircraft was 112 kt in the northeast quadrant, while the SFMR winds
peaked around 90 kt. Although the satellite intensity estimates have
fallen a bit this morning, the reduced flight-level winds support
holding the initial intensity at 100 kt for this advisory. The
minimum pressure of Lee remains 948 mb based on dropsonde data.

Lee is still moving slowly west-northwestward (290/6 kt), with
mid-level ridging established to the north and west of the
hurricane. This steering pattern is expected to change during the
next couple of days as a deep-layer trough moves across the eastern
United States and produces a weakness in this ridge. As a result,
Lee is forecast to turn northward and gradually accelerate during
the middle and latter parts of this week. The track guidance
envelope shows little cross-track spread during the first 3 days of
the forecast period, and this portion of the NHC forecast is fairly
similar to the previous one. While the core of the hurricane is
forecast to pass west of Bermuda, the large wind field of the storm
is likely to bring wind impacts to the island later this week, and
tropical storm watches could be required later today. At days 4-5,
there has been a slight westward shift in the guidance envelope, and
accordingly the NHC track forecast was nudged in that direction
toward the HCCA and TVCA aids.

Based on Lee's current satellite structure, as well as its slow
forward motion and large wind field, little near-term strengthening
is expected. Going forward, the large hurricane appears likely to
begin upwelling cooler waters along its path, and in a few days it
will encounter the cool wake left behind by recent western Atlantic
hurricanes. Thus, gradual weakening is forecast through midweek.
Later, the aforementioned trough is expected to produce stronger
deep-layer shear over Lee, and the hurricane is forecast to move
over significantly cooler waters as it passes north of the Gulf
Stream. As a result, more significant weakening is shown at days
4-5, along with completion of its extratropical transition. Despite
the weakening that is forecast, keep in mind that the expanding wind
field of Lee will produce impacts well away from the storm center.


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 tropical storm watches
could be required for the island later today.

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  12/0900Z 24.0N  65.4W  100 KT 115 MPH
 12H  12/1800Z 24.4N  66.2W  100 KT 115 MPH
 24H  13/0600Z 25.3N  67.0W  100 KT 115 MPH
 36H  13/1800Z 26.6N  67.5W   95 KT 110 MPH
 48H  14/0600Z 28.3N  67.9W   90 KT 105 MPH
 60H  14/1800Z 30.4N  68.0W   85 KT 100 MPH
 72H  15/0600Z 32.9N  67.6W   80 KT  90 MPH
 96H  16/0600Z 39.0N  66.7W   70 KT  80 MPH
120H  17/0600Z 44.5N  66.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Reinhart
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