[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 090240
TCDAT3

Hurricane Lee Discussion Number  15
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Fri Sep 08 2023

Strong southwesterly shear has taken a toll on Lee's structure.
The crews of ongoing NOAA and Air Force Reserve Hurricane Hunter
missions reported that the hurricane's eyewall has opened up, and
the satellite presentation has degraded significantly since earlier
today.  Both planes have found the minimum pressure rising during
their missions, with the latest measurements being around 963 mb.
Based on this pressure and the planes' wind measurements, Lee's
initial intensity is set at 100 kt.

Moderate-to-strong deep-layer southwesterly shear is expected to
continue for at least the next 24 hours, if not longer.  The GFS
model is the quickest to show the shear abating, but the ECMWF
now maintains shear over Lee for much of the forecast period.  Most
of the intensity guidance shows Lee weakening further during the
next 12-24 hours while the shear is at its strongest, and that is
shown in the new NHC forecast.  Despite the uncertainty in how
the upper-level pattern, and hence the shear profile, will evolve
around Lee, it is assumed that the atmospheric environment will
become at least a little more conducive for restrengthening after
24 hours.  The NHC intensity forecast blends the latest IVCN
and HCCA consensus models with the previous official forecast,
particularly after 48 hours.  Confidence in the intensity forecast
is low at the moment, although it is likely that Lee will remain a
dangerous hurricane for at least the next 5 days.

Lee's heading and speed remain 300 degrees at 11 kt.  The
mid-tropospheric ridge to the north of the hurricane is forecast to
build to the west and southwest during the next few days, which
will keep Lee on a west-northwestward course with a decrease in
speed through next Tuesday.  By Wednesday, a deep-layer trough is
forecast to amplify over the eastern United States, erode the
ridge, and cause Lee to gradually turn toward the northwest.
Although the track models agree on this general scenario, there is
disagreement on how far west Lee will get before it makes the turn.
To account for the latest suite of models, the NHC track forecast
has been shifted slightly westward on days 3 through 5, close to
the consensus aids but not as far west as the ECMWF, UKMET, and the
GEFS ensemble mean.


KEY MESSAGES:

1. Lee's core is expected to move well north of the northern
Leeward Islands, the Virgin Islands, and Puerto Rico this weekend
and early next week.

2. Dangerous surf and life-threatening rip currents are affecting
portions of the northern Leeward Islands.  These conditions
will spread westward and northward, affecting Puerto Rico,
Hispaniola, the Turks and Caicos, the Bahamas, and Bermuda
through the weekend.

3. It is way too soon to know what level of impacts, if any, Lee
might have along the U.S. East Coast, Atlantic Canada, or Bermuda
late next week, particularly since the hurricane is expected to
slow down considerably over the southwestern Atlantic.  Regardless,
dangerous surf and rip currents are expected along most of the U.S.
East Coast beginning Sunday and Monday.  Continue to monitor
updates to Lee's forecast during the next several days.


FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 19.3N  56.5W  100 KT 115 MPH
 12H  09/1200Z 20.0N  57.8W   95 KT 110 MPH
 24H  10/0000Z 20.8N  59.4W   95 KT 110 MPH
 36H  10/1200Z 21.5N  60.8W  105 KT 120 MPH
 48H  11/0000Z 22.0N  62.0W  115 KT 130 MPH
 60H  11/1200Z 22.5N  63.2W  120 KT 140 MPH
 72H  12/0000Z 22.8N  64.2W  120 KT 140 MPH
 96H  13/0000Z 23.5N  66.4W  120 KT 140 MPH
120H  14/0000Z 25.3N  67.7W  105 KT 120 MPH

$$
Forecaster Berg
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