Hurricane Georges's Landfall in the Dominican Republic: Detailed Airborne Doppler Radar Imagery

Abstract

Current understanding of landfalling tropical cyclones is limited, especially with regard to convective?scale pro?cesses. On 22 September 1998 Hurricane Georges made landfall on the island of Hispaniola, leaving behind a trail of death and devastation, largely the result of excessive rainfall, not storm surge or wind. Detailed airborne measurements were taken as part of the Third Convection and Moisture Experiment. Of particular interest are the ER?2 nadir X?band Doppler radar data, which provide a first?time, high?resolution view of the precipitation and airflow changes as a hurricane interacts with mountainous terrain. The circulation of Hurricane Georges obviously declined during landfall, evident in the rapid increase in minimum sea level pressure, the subsidence of the eyewall anvil, and the decrease in average ice concentrations in the eyewall. The eye, as seen in satellite imagery, disappeared as deep convection erupted within the eye. The main convective event within the eye, with upper?level updraft magnitudes over 20 m s?1 and microwave brightness temperatures below 100 K at 89 GHz (implying large ice concentrations), occurred when the eye moved over the Cordillera Central, the island's main mountain chain. The location, intensity and evolution of this convection indicate that it was coupled to the surface orography. The authors speculate that orographic lifting released potential energy, which had been trapped beneath the eye's subsidence inversion. It is likely that surface rain rates increased during landfall, both in the convective and in the more widespread stratiform rainfall areas over the island. Evidence for this is the increase in radar reflectivity below the bright band down to ground level. Such increase was absent offshore. This low?level rain enhancement must be due to the ascent of boundary layer air over the topography.