[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 160249
TCDAT3

Hurricane Lee Discussion Number  43
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Fri Sep 15 2023

Lee remains a very large and dangerous hurricane as it approaches
the northeast United States and Atlantic Canada. The satellite
depiction of Lee shows that the system continues to become more
asymmetric, with most of the convection displaced to the north of
the center. An earlier SSMI/S microwave pass shows thick banding on
the northern and western side of the inner core, which is where the
Air Force Hurricane Hunters found the strongest flight-level and
surface winds. The initial intensity, based on aircraft
reconnaissance data, will remain at 70 kt for this advisory.  Air
Force Hurricane Hunters will be investigating Lee again overnight.

Lee continues to wobble as it approaches the northeastern United
States and Atlantic Canada. The past few hours there has been a bit
of a north-northeast jog. Whether this is more of a wobble or a
longer-term motion is still to be determined. Global model guidance
has been hinting that this type of motion would occur as it makes
its approach towards Atlantic Canada, with a slight bend back to the
north-northwest over the next 12-18 h. The track forecast was nudged
to the right given the current motion, but it does show a
north-northwestward motion in the short term. These slight
adjustments on the final approach are minor given the very large
wind field of Lee. Once Lee makes landfall, the system is expected
to accelerate to the northeast as it moves in the flow on the east
side of an approaching trough.

Strong southerly vertical wind shear has displaced the convection to
the northern side of the system. Dry air entrainment is also
inhibiting convection on the southern and eastern side of the
circulation. These hostile environmental conditions will persist as
Lee moves over much cooler waters after it crosses the north wall of
the Gulf Stream on Saturday. Lee is already showing signs of
completing its extratropical transition, with displaced convection
and an elongated center on a recent scatterometer pass, and thus
this transition is now explicitly forecast to occur within the next
12 h. Gradual weakening is forecast throughout the period, the NHC
intensity forecast is similar to the previous, closest to the GFS.

KEY MESSAGES:

1. Hurricane conditions are possible across portions southern New
Brunswick, and much of Nova Scotia on Saturday within the Hurricane
Watch area.  Tropical storm conditions and coastal flooding are
expected to begin in southern New England within the Tropical Storm
Warning area very soon, and spread northward along the coast of
New England and over portions of Atlantic Canada through Saturday.
These conditions are likely to lead to downed trees and potential
power outages.

2. Heavy rainfall from Lee may produce localized urban and small
stream flooding in portions of eastern Maine, New Brunswick and
western Nova Scotia Saturday.


FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 39.5N  65.8W   70 KT  80 MPH
 12H  16/1200Z 41.7N  66.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 24H  17/0000Z 44.5N  65.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 36H  17/1200Z 47.3N  63.3W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  18/0000Z 50.6N  58.1W   40 KT  45 MPH...POST-TROP/EXTRATROP
 60H  18/1200Z 53.0N  50.4W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  19/0000Z 54.3N  41.3W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  20/0000Z...DISSIPATED

$$
Forecaster Kelly/Brown
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