000 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