Inner shelf response to Tropical Storm Floyd

Abstract

A continuously operated coastal observatory off the southern coast of New Jersey provides an opportunity to study both long‐term trends and episodic events. On the evening of 16 September 1999, Tropical Storm Floyd moved up the New Jersey coast directly over the observatory. The response of the inner shelf is characterized using a depth‐averaged (DA) and surface layer (SL) model in conjunction with direct observations. During the storm, the DA model was more representative of the observed response. While there was a peak in the near‐inertial band of the depth average current, the response was not the typical clockwise ringing response seen in deepwater stratified regions. Instead the shallow, well‐mixed inner shelf responded with an alongshore current oscillation balanced by the alongshore pressure gradient and bottom stress. The increased influence of bottom friction damps the typical inertial tail seen in deeper ocean responses and shortens the relaxation phase from several days to hours. Immediately following the storm, the surface layer model better represents the observed currents. It appears that the excessive rainfall associated with the storm and the resulting freshening of the inner shelf isolate the surface layer from the effect of bottom friction. The large waves and currents associated with the storm increase the potential for a sediment resuspension and transport event. Unlike the typical nor'easter in which the transport in this location is alongshore toward the south and onshore, the currents coinciding with the largest waves are alongshore toward the south but with an offshore component.