Detailed modeling of recent severe storm tides in estuaries of the New York City region

Detailed simulations, comparisons with observations, and model sensitivity experiments are presented for the August 2011 tropical cyclone Irene and a March 2010 nor'easter that affected the New York City (NYC) metropolitan area. These storms brought strong winds, heavy rainfall, and the fourth and seventh highest gauged storm tides (total water level), respectively, at the Battery, NYC. To dissect the storm tides and examine the role of various physical processes in controlling total water level, a series of model experiments was performed where one process was omitted for each experiment, and results were studied for eight different tide stations. Neglecting remote meteorological forcing (beyond similar to 250 km) led to typical reductions of 7-17% in peak storm tide, neglecting water density variations led to typical reductions of 1-13%, neglecting a parameterization that accounts for enhanced wind drag due to wave steepness led to typical reductions of 3-12%, and neglecting atmospheric pressure gradient forcing led to typical reductions of 3-11%. Neglecting freshwater inputs to the model domain led to reductions of 2% at the Battery and 9% at Piermont, 14 km up the Hudson River from NYC. Few storm surge modeling studies or operational forecasting systems incorporate the estuary effects of freshwater flows and water density variations, yet joint omission of these processes for Irene leads to a low-bias in storm tide for NYC sites like La Guardia and Newark Airports (9%) and the Battery (7%), as well as nearby vulnerable sites like the Indian Point nuclear plant (23%).