Hurricane Floyd Rainfall in New Jersey

After ravaging portions of the Bahamas and dropping extremely heavy rain on already saturated ground in eastern North Carolina, Hurricane Floyd unleashed torrential rains on central and northern New Jersey. This led to record flooding within several NJ river systems, including the Raritan basin, where rivers crested at as much as 14 feet above flood stage, several feet above previous record crests. Thousands of individuals were evacuated from homes that had water up to the second floor, business districts were severely damaged, and a water plant serving over a million people was inundated and put out of service for almost a week.

Precipitation observations for the September 15-16, 1999 period have been collected from close to 150 stations across New Jersey. All told, at least one station in 10 of New Jersey's 21 counties reported over 8 inches of rain from Floyd, with at least one site in six of these counties accumulating over 10 inches. Within the Raritan basin, 8-10 inches, with locally as much as 11 inches, fell in the western two thirds (headwaters) of the basin.

This contribution will discuss the atmospheric conditions during this event and the quality of the observations made. Maps and tables of Floyd rainfall will be shown, with particular attention paid to the Raritan River basin. A comparison of station reports to radar estimates will also be made. Finally, Floyd rainfall will be compared with totals from Tropical Storm Doria in 1971. Doria led to the previous 20th century flood of record on the Raritan. The latter is of particular interest to hydrologists and others, as attempts are made to determine whether the September 1999 flood exceeded the 1971 event due to: 1) Floyd producing more rainfall, 2) Floyd rains falling over a shorter period, 3) considerable suburban development in the Raritan basin over the past several decades influencing the timing and quantity of runoff, or 4) a combination of all the above.

This investigation is part of "The Great Raritan Flood Project" an interdisciplinary effort being conducted by students, faculty and staff in the Rutgers University Department of Geography. Other contributors are exploring the hydrologic data in greater detail, investigating property loses and populations that suffered the greatest loses, and evaluating the warning, response and recovery aspects of the devastating flooding.