Radar-derived rainfall estimates for Hurricane Floyd over New Jersey

On September 16, 1999, Hurricane Floyd struck the Atlantic seaboard from the Carolinas northward through New England. Although hurricane force winds were limited to more southern areas, Floyd produced very heavy rain and associated flooding over much of its entire track along the East Coast. Besides devastating floods over already saturated eastern North Carolina, one of the hardest hit areas was in northern New Jersey. Numerous sites there reported storm totals greater than 203 mm (8 inches) of rain, up to a maximum of 367 mm (14.45 inches). These amounts produced record floods in the Raritan basin and several other North Jersey river systems.

This study examines the value of quantitative precipitation estimates from the National Weather Service's WSR-88D Doppler radar (NEXRAD) over New Jersey during hurricane Floyd. Hourly radar-derived rainfall estimates are compared with a network of approximately 40 rain gages in the hardest hit area of northern New Jersey. Rainfall estimates derived from the standard NEXRAD Z-R relation are compared with estimates using a Z-R relation designed for tropical systems. Estimates derived using the WSR-88D radar at Ft. Dix, New Jersey (KDIX) are compared to estimates from the radar at Upton, New York (KOKX). The role of these estimates in the issuance of real-time operational Flood Warnings and Flash Flood Warnings is evaluated.