[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 070245
TCDAT3

Hurricane Lee Discussion Number   7
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Wed Sep 06 2023

Lee has an asymmetric structure this evening, with the bulk of the
convective activity located to the east of the center.  Dvorak
estimates from TAFB and SAB were a pair of T4.0s/65 kt, but
objective Dvorak estimates from UW-CIMSS are a little higher.
Therefore, Lee's initial intensity is set at 70 kt.

The initial motion remains west-northwestward, or 295/12 kt, with
Lee situated to the south of the subtropical ridge.  Ridging is
expected to build westward, and even out ahead of the hurricane
over the southwestern Atlantic, during the next 5 days.  As a
result, Lee is likely to maintain a west-northwestward trajectory
but gradually slow down beyond day 2, with its forward speed
decreasing to about 7 kt by day 5.  The new NHC track forecast
is right on top of the previous prediction during the first
3 days of the forecast.  After that, the official forecast has been
nudged westward, leaning toward the latest TVCX and HCCA consensus
aids.  The track model envelope continues to indicate that the
core of Lee will pass to the north of the northern Leeward
Islands.  However, interests in those islands should continue to
monitor Lee's forecasts as the typical three-day NHC track error is
about 90 n mi, and the northernmost Leeward Islands currently have
a 1-in-4 chance of experiencing sustained tropical-storm-force
winds on the southern side of the storm.

Global model fields show a well-defined upper-level anticyclone
developing over Lee during the next 24 hours and persisting over
the hurricane into the weekend, which should keep the deep-layer
shear quite low.  In addition, oceanic heat content values will
double along Lee's track during the next 3 days.  As a result,
rapid intensification (RI) is forecast to begin on Thursday, and
following the previous forecast, a 65-kt increase in strength is
predicted during the next 3 days, bringing Lee to high-end category
4 intensity.  This forecast lies close to the HAFS dynamical model
and HCCA consensus aid solutions, and it is also supported by very
high RI probabilities from the DTOPS scheme for the 36-, 48-, and
72-hour forecast periods.  Fluctuations in intensity are likely by
days 4 and 5 due to potential eyewall replacements, but Lee is
still expected to be a large and dangerous hurricane over the
southwestern Atlantic early next week.


KEY MESSAGES:

1. Lee is forecast to become a major hurricane by early Friday,
with its core moving north of the northern Leeward Islands, the
Virgin Islands, and Puerto Rico this weekend into early next week.
There is the potential for tropical storm conditions to occur on
some of these islands over the weekend, and interests there should
monitor future updates to Lee's forecast.

2. Swells generated by Lee are expected to reach portions of the
Lesser Antilles on Friday, and the British and U.S. Virgin Islands,
Puerto Rico, Hispaniola, the Bahamas, and Bermuda this weekend.
These swells are likely to cause life-threatening surf and rip
current conditions.


FORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 15.4N  47.7W   70 KT  80 MPH
 12H  07/1200Z 16.1N  49.5W   75 KT  85 MPH
 24H  08/0000Z 17.0N  51.9W   85 KT 100 MPH
 36H  08/1200Z 18.1N  54.2W  105 KT 120 MPH
 48H  09/0000Z 19.1N  56.5W  120 KT 140 MPH
 60H  09/1200Z 20.1N  58.5W  130 KT 150 MPH
 72H  10/0000Z 20.8N  60.3W  135 KT 155 MPH
 96H  11/0000Z 22.0N  63.5W  130 KT 150 MPH
120H  12/0000Z 23.0N  66.1W  125 KT 145 MPH

$$
Forecaster Berg
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