Potential Tropical Cyclone Sixteen Forecast Discussion Number 3

By | September 22, 2023

WTNT41 KNHC 220252

Potential Tropical Cyclone Sixteen Discussion Number   3
NWS National Hurricane Center Miami FL       AL162023
1100 PM EDT Thu Sep 21 2023

Nighttime proxy-visible satellite imagery suggests that the center
of the low pressure system off the southeastern U.S. coast has
become better defined this evening.  Nearly all of the associated
deep convection remains oriented in a curved band extending around
the northern and eastern sides of the circulation, although a few
convective elements are beginning to fill in on the back side of
the system as well.  Based on 1-minute wind observations from NOAA
buoy 41002 and ship reports, the initial intensity is raised to 35
kt, with all tropical-storm-force winds currently north of the
center on the north side of an attached warm front.

The center does not appear to have moved much since the time it 
became better defined.  Based on previous fixes, the current motion 
is estimated to be north-northeastward (015 degrees) at 3 kt.
The dynamical guidance indicates that the center should begin moving
northward--or re-form to the north--overnight, with a northward or
north-northwestward motion continuing through Sunday morning.  This
forecast track brings the center of the low inland across eastern
North Carolina on Saturday, and then across the southern Chesapeake
Bay and the Delmarva Peninsula Saturday night and Sunday.  Except
for the errant HWRF (which appears too far west), the rest of the
guidance is tightly clustered, and the NHC forecast is near the
middle of the envelope.  This new forecast is a bit east of the
previous prediction, mainly for the portion of the track over land.

Baroclinic processes associated with a sharp upper-level trough to
the west of the low are expected induce strengthening, and the NHC
intensity forecast is close to the GFS, ECMWF, and HCCA solutions,
bringing the maximum winds to 50 kt in 24-36 hours before the
center reaches the North Carolina coast.  In addition, simulated
satellite imagery suggests there could be an increase of deep
convection near the low's center by Friday evening, and phase-space
diagrams show the system just barely entering the deep warm core
regime.  Therefore, transition to a tropical cyclone is shown by 24
hours, although there still is some uncertainty on that occurrence
due to frontal boundaries still in the area.  Weakening is forecast
after the center moves onshore, and the system is expected to
become extratropical again by 60 hours.  An official forecast is
only provided out through 72 hours since global model fields
show the low becoming absorbed by the associated frontal boundary
off the New Jersey coast by 96 hours.

Key Messages:

1. Low pressure off the southeastern U.S. coast is producing
tropical-storm-force winds and is forecast to strengthen further
before it reaches the coast of North Carolina on Saturday.  Tropical
storm conditions are expected along portions of the southeastern and
mid-Atlantic U.S. coasts within the Tropical Storm Warning area
beginning on Friday 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 Friday 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.


INIT  22/0300Z 29.5N  75.3W   35 KT  40 MPH...POTENTIAL TROP CYCLONE
 12H  22/1200Z 31.2N  75.5W   45 KT  50 MPH...POTENTIAL TROP CYCLONE
 24H  23/0000Z 32.5N  76.1W   50 KT  60 MPH...TROPICAL CYCLONE
 36H  23/1200Z 34.4N  76.5W   50 KT  60 MPH
 48H  24/0000Z 36.4N  76.6W   40 KT  45 MPH...INLAND
 60H  24/1200Z 37.9N  76.2W   30 KT  35 MPH...POST-TROP/EXTRATROP
 72H  25/0000Z 39.0N  75.2W   30 KT  35 MPH...POST-TROP/EXTRATROP
 96H  26/0000Z...DISSIPATED

Forecaster Berg

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