[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 150250
TCDAT3

Hurricane Lee Discussion Number  39
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Thu Sep 14 2023

Observations from an Air Force Reserve Unit Hurricane Hunter
aircraft indicate that Lee's eyewall is not well defined, and this
is also suggested by geostationary satellite and microwave imagery.
Although the peak 700 mb flight-level winds reported by the plane
were near 93 kt, the highest SFMR-observed surface winds were 72 kt.
Thus the winds aloft in the hurricane are not being transported
very effectively to the surface.  This is not surprising, since the
central deep convection is no longer very strong.  The current
intensity is kept at 75 kt based on the aircraft data, which is
well above the Dvorak satellite estimates.

Lee wobbled a bit to the northeast early this evening, but the
longer-term motion appears to be just east of north, or around
010/12 kt.  The system should move generally northward at a faster
forward speed, on the west side of a mid-level ridge, during the
next day or so.  A slight bend to the left is likely late Friday as
the cyclone interacts with a mid-level trough.  By late Saturday,
Lee should begin to turn toward the north-northeast with the center
passing near or over western Nova Scotia.  Then, Lee is forecast to
turn northeastward over Atlantic Canada.  The track guidance remains
in good agreement through 72 hours, and the official forecast is
basically an update of the previous one.

South-southwesterly shear is predicted to increase significantly
over Lee during the next couple of days.  This, along with cooler
SSTs, particularly after the system moves north of 40N latitude,
should result in weakening.  However, baroclinic processes could
help the cyclone maintain its intensity, or at least slow the
weakening rate.  The official intensity forecast is above the model
guidance for this reason.  In 48 hours, simulated satellite imagery
shows an asymmetric cloud structure characteristic of an
extratropical cyclone.  Regardless of when extratropical transition
actually occurs, however, Lee should remain a very large and
dangerous cyclone through landfall.


KEY MESSAGES:

1. Tropical storm conditions, heavy rainfall, and high surf will
continue to impact Bermuda through Friday morning, 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 is in effect for that
area.  Tropical storm conditions and coastal flooding are expected
to begin in southern New England on Friday afternoon, and spread
northward along the coast of New England and over portions of
Atlantic Canada through Saturday where Tropical Storm warnings are
in effect.

3. Heavy rainfall from Lee may produce localized urban and small
stream flooding across eastern New England and into portions of New
Brunswick and Nova Scotia from Friday night into Saturday night.


FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 32.9N  67.6W   75 KT  85 MPH
 12H  15/1200Z 35.0N  67.3W   75 KT  85 MPH
 24H  16/0000Z 38.4N  66.6W   75 KT  85 MPH
 36H  16/1200Z 41.6N  66.6W   65 KT  75 MPH
 48H  17/0000Z 44.3N  66.0W   60 KT  70 MPH...POST-TROP/INLAND
 60H  17/1200Z 47.0N  63.6W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  18/0000Z 49.6N  59.1W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  19/0000Z 54.5N  42.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  20/0000Z...DISSIPATED

$$
Forecaster Pasch
This weather bulletin was brought to you by:
www.nashvilleweather.net