Eye and Eyewall Traits as Determined with the NOAA WP-3D Lower-Fuselage Radar

Abstract

Eye and eyewall traits were ascertained for 209 images from 37 tropical cyclones (TCs) using the lower-fuselage 5.6-cm radar, aboard the two National Oceanic and Atmospheric Administration WP-3Ds. These TCs were almost entirely from the Atlantic basin and were sampled from 1997 to 2012. For the eye these traits included area, maximum diameter, and roundness; for the eyewall the traits included area, completeness, maximum width, maximum reflectivity value and location, number of local reflectivity maxima, and mean rain rate. These variables were compared to TC intensity and motion characteristics from the best-track dataset, and environmental characteristics from the Statistical Hurricane Intensity Prediction Scheme. Interrelationships between eyewall features revealed that eyewall reflectivity features became more homogeneous as eye and eyewall areas shrank, and maximum reflectivity and rain rate increased as the eyewall became wider and more complete. As the TC intensified, the eye area decreased, while the eyewall area increased due to increasing completeness and width. Rain rate was also found to be higher for faster-moving TCs. Stronger vertical shear of the horizontal wind was found to be associated with more asymmetric eyewall reflectivity. The maximum reflectivity value occurred most often on the downshear side of the eyewall, and to the right of the storm motion, verifying prior research. There were no relationships found between the reflectivity and sea surface temperature or environmental relative humidity. A schematic incorporating typical eye and eyewall traits is presented.