Investigation of the Dynamics Associated with a Sudden Southward Deflection of Hurricane Florence (2018) After Landfalling

Hurricane Florence (2018) was a Category 1 storm that moved slowly across the eastern coast of the United States. The hurricane originated from an African Easterly Wave over Africa, then developed into a tropical depression off the coast of Africa, and made landfall on September 14^th near Wrightsville Beach, NC. Florence produced eight to eleven feet of storm surge along the coast and dropped tremendous amounts of rain. A distinctive feature about Hurricane Florence is its track shape, the “L-shaped” track. After making landfall, Florence made an abrupt southward turn and continued moving southwesterly for about 3 days and then turned north/northeasterly as it further dissipated. This study focuses on the dynamic features that are attributed to Florence’s track deflection and the storm’s steering. The data utilized in this study include the observation data from the National Hurricane Center’s (NHC) Best Track (HURDAT2), the ERA5 reanalysis data of European Centre for Medium-Range Weather Forecasts (ECMWF), and the simulation data from using the WRF (Weather Research and Forecasting) model. Multiple simulations were conducted to establish a control case, that captures the track deflection with minimum error. The dynamic features investigated in this study that attributed to hurricane’s track deflection and the storm’s steering include the vorticity, potential vorticity (PV), wind, streamlines, and geopotential height fields. The positive relative vorticity tendency is consistent with the storm’s movement. The wind and the streamlines outside the rim of the hurricane match well with the track’s turning. It is expected that the storm will move toward the maximum vorticity regions, which was associated with the eastward moving shortwave trough located in lower troposphere and to the west of the storm during Florence’s landfall. Studies on track deflection are important because it will help extend the lead time for track forecasts.