[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 130853
TCDAT3

Hurricane Lee Discussion Number  32
NWS National Hurricane Center Miami FL       AL132023
500 AM AST Wed Sep 13 2023

Lee's structure is very gradually declining in organization.  The
hurricane has a ragged but somewhat elliptical 25-30 n mi wide eye,
but deep convection has become eroded a bit within the western
semicircle, possibly due to some moderate westerly shear.  In
addition, a 0607 UTC AMSR-2 microwave pass showed that the eyewall
was open on the southwest side at that time.  Subjective and
objective satellite estimates range from 90-105 kt, so Lee's
initial intensity remains 100 kt for now.

The hurricane is very slowly making its turn around a west-central
Atlantic mid-level high, with its motion now northwestward at
325/5 kt.  The track guidance is tightly clustered during the next
2 days or so, showing Lee turning and accelerating toward the
north-northwest and north between the high and a shortwave trough
swinging across the Great Lakes region.  Lee's core is forecast to
pass west of Bermuda in 36-48 hours, but tropical storm conditions
are likely to begin there late tonight or early Thursday due to the
hurricane's large wind field.  On days 3 and 4, Lee is expected to
maintain a general northward track offshore the northeastern U.S.
However, the global models are suggesting that the hurricane
will interact with a remnant mid-level trough over the mid-Atlantic
states, causing Lee to possibly bend just west of due north while
it moves across the Gulf of Maine.  Under the assumption that the
global models will have a better handle on this mid-latitude
pattern as compared to the regional hurricane models, the NHC track
forecast is close to a consensus of the GFS and ECMWF models (GFEX)
on days 3, 4, and 5, and therefore ends up being a bit west and
then north of the previous prediction on those days.

A number of factors--including Lee's broad structure, increasing
shear, and potential upwelling of cooler waters--are likely to lead
to a very gradual decrease in the hurricane's maximum winds during
the next 3 days or so.  In addition, Lee is likely to begin
extratropical transition in 2-3 days, with that process expected to
be complete just before the cyclone's center reaches the coast of
Maine, New Brunswick, or Nova Scotia in about 4 days.  That said,
Lee's expected post-tropical transition will not diminish potential
wind, rain, and coastal flooding impacts in New England and Atlantic
Canada due to the system's broad wind field.

It should again be noted that the 34- and 50-kt wind speed
probabilities beyond 36 hours in the text and graphical products 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 late tonight or early Thursday,
and a Tropical Storm Warning is in effect for the island.

3. There is an increasing risk of wind, coastal flooding, and rain
impacts from Lee in portions of New England and Atlantic Canada
beginning on Friday and continuing through the weekend.  Watches may
be required for portions of these areas later today or tonight.
Due to Lee's large size, hazards will extend well away from the
center, and there will be little to no significance on exactly where
the center reaches the coast.


FORECAST POSITIONS AND MAX WINDS

INIT  13/0900Z 25.7N  67.1W  100 KT 115 MPH
 12H  13/1800Z 26.6N  67.6W   95 KT 110 MPH
 24H  14/0600Z 28.4N  68.1W   90 KT 105 MPH
 36H  14/1800Z 30.5N  68.3W   85 KT 100 MPH
 48H  15/0600Z 33.0N  68.0W   80 KT  90 MPH
 60H  15/1800Z 36.1N  67.4W   75 KT  85 MPH
 72H  16/0600Z 39.6N  67.3W   70 KT  80 MPH
 96H  17/0600Z 45.2N  67.3W   50 KT  60 MPH...POST-TROP/INLAND
120H  18/0600Z 51.0N  61.4W   35 KT  40 MPH...POST-TROP/INLAND

$$
Forecaster Berg
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