[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 220834
TCDAT1

Potential Tropical Cyclone Sixteen Discussion Number   4
NWS National Hurricane Center Miami FL       AL162023
500 AM EDT Fri Sep 22 2023

The low pressure system off the southeast U.S. coast is gradually
organizing and strengthening this morning.  The cyclone is
developing subtropical characteristics with deep convection
consolidating on the system's north side and the center gaining
definition, but there are still some frontal features associated
with it.  NOAA buoy 41002 well off the coast of Cape Hatteras has
seen a significant pressure drop during the past several hours, and
the latest report was down to 1002 mb with 30-kt winds.  A
saildrone measured winds of 32 kt well northeast of the center
several hours ago.  Based on these pressure and wind observations as
well as satellite intensity estimates, the initial intensity is
increased to 45 kt.  Based on recent trends, it seems likely that
the low will become a subtropical or tropical cyclone later today.

The system has been moving erratically overnight, but recent
satellite images suggest that it is now moving northward at about 7
kt.  A northward to northwestward motion is expected during the next
couple of days as the system moves on the west side of a subtropical
high, taking the cyclone inland over eastern North Carolina early
Saturday and over portions of the Mid-Atlantic Saturday night
and Sunday. The NHC track forecast is quite similar to the previous
one and not far from the GFS and ECMWF models.

The notable strengthening that has occurred overnight is due to a
combination of baroclinic influences from the mid- to upper-level
trough just to the west of the system and the warm Gulf Stream
waters.  The system will likely strengthen a little more before it
reaches the coast of North Carolina.  After landfall, land
interaction, dry air, and strong shear should lead to weakening and
cause the system to transition back to an extratropical low in a
couple of days.

It should be noted that the cyclone has a large wind field, and
tropical-storm-force winds will begin well ahead of the center.

Key Messages:

1. Low pressure off the southeastern U.S. coast is producing
a large area of tropical-storm-force winds and is forecast to
strengthen further before it reaches the coast of North Carolina
early Saturday.  Tropical storm conditions are expected along
portions of the southeastern and mid-Atlantic U.S. coasts within
the Tropical Storm Warning area beginning later this morning and
continuing into Saturday night.

2. There is a danger of life-threatening storm surge inundation
over portions of eastern North Carolina and southeastern Virginia,
including Pamlico and Albemarle Sounds, and the lower Chesapeake
Bay, where Storm Surge Warnings are in place.  Residents in these
areas should follow advice given by local officials.

3. Heavy rainfall from this system could produce localized urban
and small stream flooding impacts across the eastern mid-Atlantic
states from North Carolina to New Jersey through Sunday.

4.  Swells generated by this system will affect much of the U.S.
east coast through the weekend, likely causing life-threatening
surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  22/0900Z 30.5N  75.0W   45 KT  50 MPH...POTENTIAL TROP CYCLONE
 12H  22/1800Z 31.6N  75.8W   50 KT  60 MPH...TROPICAL CYCLONE
 24H  23/0600Z 33.4N  76.5W   50 KT  60 MPH
 36H  23/1800Z 35.3N  76.8W   45 KT  50 MPH...INLAND
 48H  24/0600Z 37.0N  76.9W   35 KT  40 MPH...INLAND
 60H  24/1800Z 38.3N  76.3W   30 KT  35 MPH...POST-TROP/EXTRATROP
 72H  25/0600Z 39.0N  75.2W   30 KT  35 MPH...POST-TROP/EXTRATROP
 96H  26/0600Z...DISSIPATED

$$
Forecaster Cangialosi
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