Dual-doppler analyses of mesovortices in a hurricane rainband

The US Weather Research Program identified landfalling tropical cyclones as a major focus for research. In 1998 the Hurricane Research Division (HRD) of NOAA's Atlantic Oceanographic and Meteorological Laboratory coordinated experiments with other agencies and university groups in Hurricanes Bonnie, Earl and Georges. On these flights airborne Doppler radar data were collected to combine with WSR-88D radar data in three-dimensional analyses to document evolution of tropical cyclones as they make landfall, and to provide data for testing WSR-88D tropical cyclone algorithms.

Hurricane Bonnie made landfall near Wilmington, North Carolina, as a Category 2 hurricane on 26 August. There were two HRD missions near the time of landfall. The first flight concentrated on examining the structure of the spiral rainbands and the second flight surveyed the hurricane as it interacted with the coast. During the flights there was a vigorous rainband ~180 km NE of the center with several mesocyclones (as identified on the Morehead City, North Carolina, WSR-88D) that later produced confirmed tornadoes on land. Both NOAA aircraft had to deviate around strong cells in this band, between 1540 and 1830 UTC, and those deviations resulted in small Doppler analysis boxes enclosing some of the mesocyclones. A companion paper (Spratt et al) uses dropsondes and adjacent radiosondes to describe the local environment in which the Bonnie mesocyclones were embedded, and in this paper we will present windfield analyses, from combining WSR-88D and airborne Doppler radar data, that provide the three dimensional structure of the mesocyclones. The Doppler data are too coarse to capture the actual tornadoes, but the parent mesoscale circulations are clearly resolved.