[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 140248
TCDAT3

Hurricane Lee Discussion Number  35
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Wed Sep 13 2023

Both NOAA and Air Force Reserve Unit Hurricane Hunter aircraft have
been investigating Lee this evening.  They found that the central
pressure has not changed much since earlier today, and that the
hurricane still had concentric eyewalls, but these were partially
open over portions of the western quadrant.  The Air Force
plane measured  700 mb flight-level winds as high as 105 kt and
the NOAA plane found winds as high as 107 kt at a flight level of
8000 ft.  Tail Doppler radar velocities from the NOAA plane were
near 100 kt at elevations of 0.5 km.  These observations support
maintaining the intensity at 90 kt for this advisory.  Satellite
imagery also suggests that the eyewall is not fully closed but
there is fairly intense inner-core convection.

There has been a (likely temporary) decrease in forward speed and
the initial motion is just west of due north or 350/8 kt.  The
steering scenario for the hurricane is essentially unchanged from
the previous few advisories.  A 500-mb trough moving into the
northeastern U.S. and a mid-level ridge near eastern Atlantic
Canada should cause Lee to move generally northward at a faster
forward speed during the next couple of days.  A slight bend to the
left is likely around 48 hours while the tropical cyclone interacts
with the trough.  This will likely bring the center of Lee close to
southeastern New England late Friday before it moves near or over
Maine and Atlantic Canada later in the weekend.  The official track
forecast is similar to the previous one and closely follows both the
simple and corrected dynamical consensus guidance.

Over the next couple of days, Lee will encounter significantly
increasing vertical wind shear and somewhat drier mid- to low-level
air.  Sea surface temperatures along the projected track decrease
sharply north of around 40N latitude. These conditions should cause
weakening, but since the hurricane has such a large circulation, the
weakening will likely be slow.  The NHC intensity forecast is near
or above the highest available model guidance.  Notwithstanding,
there is still high confidence that Lee will be a large and
dangerous cyclone when it moves near or over land on Saturday.

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. Tropical storm conditions, heavy rainfall, and high surf are
expected to impact Bermuda beginning early Thursday, and a Tropical
Storm Warning is in effect for the island.

2. Hurricane conditions and coastal flooding are possible in
portions of eastern Maine, southern New Brunswick, and western Nova
Scotia on Saturday, and a Hurricane Watch has been issued for that
area.  Heavy rainfall in these areas may produce localized urban
and small stream flooding from Friday night into Saturday night.

3. There is the potential for life-threatening storm surge flooding
in portions of southeastern Massachusetts, including Cape Cod and
Nantucket, late Friday and Saturday, where a Storm Surge Watch has
been issued.

4. Tropical storm conditions are possible over a large portion of
coastal New England, including Cape Cod, Nantucket, Martha's
Vineyard, Block Island, and portions of Atlantic Canada, where a
Tropical Storm Watch has been issued.


FORECAST POSITIONS AND MAX WINDS

INIT  14/0300Z 28.0N  67.7W   90 KT 105 MPH
 12H  14/1200Z 29.6N  68.1W   90 KT 105 MPH
 24H  15/0000Z 31.9N  68.0W   85 KT 100 MPH
 36H  15/1200Z 34.8N  67.2W   80 KT  90 MPH
 48H  16/0000Z 37.7N  66.5W   75 KT  85 MPH
 60H  16/1200Z 41.0N  66.7W   65 KT  75 MPH
 72H  17/0000Z 44.0N  66.3W   60 KT  70 MPH
 96H  18/0000Z 49.4N  60.9W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  19/0000Z 53.7N  50.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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