Coastal Radar Observations and Impacts of Hurricanes Florence and Michael (2018)

Two significant hurricane landfalls in 2018 from Florence and Michael caused loss of life and major damage to coastal regions in the southeast U.S., including impacts well inland from the landfall location. While both storms had multiple hazards from strong winds, heavy rain, and powerful storm surge, the most significant damage from each storm was due to different impacts from water and winds. A slow moving Hurricane Florence caused extensive flooding with a peak total rainfall of 913 mm over several days in the Carolinas, while a rapidly intensifying Hurricane Michael caused extreme wind damage in coastal Florida and inland Georgia. The U.S. coastal NEXRAD network observed both of these storms and collected valuable data on their evolution and impacts using dual-polarization and Doppler radar technologies. Polarimetric radar observations of Florence allow for accurate rainfall rate and drop size distribution (DSD) estimates, with heavy rain impacts largely occurring in the outer rainbands away from the center. The variability in precipitation intensity and DSDs from Florence will be presented and compared with Hurricane Harvey (2017), indicating some common and some distinct microphysical characteristics. In comparison, Hurricane Michael’s damage was most significant closer to the center due to category-4 sustained winds in the eyewall. Radar observations indicated a polygonal eyewall structure and rapidly intensifying Doppler velocities as it approached the coast over very warm ocean temperatures. A single-Doppler wind retrieval using the Generalized Velocity Track Display (GVTD) technique is used to analyze the axisymmetric and asymmetric kinematic evolution. Polarimetric and Doppler radar observations illustrate the differing impacts from these recent disasters, and emphasize the challenges in both forecasting and communication of multiple tropical storm hazards.