[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 130242
TCDAT3

Hurricane Lee Discussion Number  31
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Tue Sep 12 2023

Geostationary satellite images show that Lee has a large eye about
40 n mi in diameter surrounded by very cold-topped central
convection.  There are numerous convective banding features,
especially over the northern portion of the circulation.  The
cirrus-level outflow pattern is fairly symmetric at this time,
suggesting that the vertical wind shear over the system is still
low.  The intensity estimate is held at 100 kt for this advisory,
which is a blend of subjective and objective satellite estimates
from TAFB, SAB, and UW/CIMSS.  The objective intensity estimates
are generally a little higher than the subjective values.

Lee continues to move on a generally northwestward heading, with a
motion estimate of 320/6 kt, on the southwestern side of a
mid-level anticyclone.  Over the next couple of days, a 500-mb
trough moving through the eastern United States should induce a
northward turn with some increase in forward speed.  Even though
the predicted track has the center of the hurricane passing well to
the west of Bermuda, Lee's very large wind field should result in
tropical storm conditions spreading over the island by late
Wednesday or early Thursday.  In the 3 to 4 day time frame, the
model guidance suggests just a slight leftward bend in the track
while Lee interacts with the trough.  There has been little change
to the NHC forecast track, which remains close to the corrected and
simple model consensus predictions.  After 96 hours, Lee should
turn northeastward and east-northeastward in the mid-latitude
westerlies.

Gradual weakening is anticipated during the next few days days
while Lee moves over cooler waters and encounters high vertical
wind shear.  However the system is likely to remain a large and
dangerous hurricane while it approaches the coast.  If Lee moves
faster than forecast over the colder waters north of the Gulf
Stream, it will likely retain more of its strength when it reaches
land.  Around 96 hours, simulated satellite imagery from the global
models show the appearance of an extratropical cyclone with
decreased convection and an asymmetric cloud pattern.

It should again be noted that 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. Tropical storm conditions, heavy rainfall, and high surf are
expected to impact Bermuda beginning Wednesday night or early
Thursday, and a Tropical Storm Warning has been issued 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  13/0300Z 25.3N  66.7W  100 KT 115 MPH
 12H  13/1200Z 26.1N  67.2W  100 KT 115 MPH
 24H  14/0000Z 27.7N  67.8W   95 KT 110 MPH
 36H  14/1200Z 29.7N  68.2W   90 KT 105 MPH
 48H  15/0000Z 32.1N  67.9W   80 KT  90 MPH
 60H  15/1200Z 35.0N  67.1W   75 KT  85 MPH
 72H  16/0000Z 38.0N  66.6W   75 KT  85 MPH
 96H  17/0000Z 44.0N  66.4W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  18/0000Z 48.5N  62.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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