Undergraduate Research and Creativity

URECA

2007-2008

An Evaluation of the Ambient Conditions Favoring Major Storm Surge

Katherine Rojowsky and Brian A. Colle
School of Marine and Atmospheric Sciences

A large fraction of the New York/ New Jersey metropolitan region is less than 5 m above sea level; therefore, much of the area is vulnerable to coastal flooding during major storm events. This was evident during the Nor'easter of 1992, in which a 1.7 m storm surge resulted in significant flooding in the New York City (NYC) area. In order to improve forecasting of these events, more understanding of the atmospheric conditions that favor storm surges around NYC is needed. We hypothesized that many storm surge events for NYC have similar storm (cyclone) tracks and evolution of the winds before and during the event. In particular, we are interested in the relationship between wind direction, strength, and duration during the more significant surge events.

In order to understand how the winds evolve at New York City during the more significant storm surge events, hourly surface observations at John F. Kennedy Airport were obtained for the 50 largest storm surge events since 1979 at The Battery, NYC. The surface wind speed and direction were analyzed 48 hours leading up to the time of maximum surge and 24 hours after the maximum surge. In addition, the tracks of the surface cyclones were obtained by identifying the minimum in central pressure at the surface every 3-h using the North American Regional Reanalysis (NARR) dataset.

The months of December and January have the largest frequency of maximum surge events at the Battery (21 out of the top 50 cases). At the time of maximum surge, there is a well-developed cyclone situated around the New Jersey coast. However, the track of the cyclones vary substantially, with some storms tracking northeastward offshore along the coast as a classical nor-easter, while others originate over the southeast U.S.. Most of the tropical cyclones track northward and parallel to the coast towards Long Island. The wind speeds increase from approximately 10 m s^-1 24-h prior to the surge to 15-20 m s^-1 at the height of maximum surge. The average wind direction steadily turns from the southeast (120^o) to more northeasterly (75^o) at John F. Kennedy airport during the 24 h period leading up to maximum surge at the Battery. There is a sudden shift to the southwest within 10 h after the surge maximum. The northeasterly wind direction prior to the maximum surge favors a storm surge in NYC because surface wind stress pulls water towards the concave coastline of the New York and New Jersey, while Ekman transport acting to the right of the wind helps pull water towards New York Harbor and the Long Island coast.