New York City Storm Surges Depend on Tidal Levels

STONY BROOK, New York, August 24, 2008 (ENS) – A new high-resolution storm surge modeling system developed by scientists at Stony Brook University will better be able to predict flood levels and when flooding will occur in the New York metropolitan area, according to a report in the most recent issue of the “Bulletin of the American Meteorological Society.”

The report warns that flooding is dependent not just upon the intensity of the tropical storm, hurricane, or nor’easter, but also on the local phase of the tide at the time of the storm.

This information is crucial to emergency managers when they are planning for impending storms.

A team led by Brian Colle, associate professor in the School of Marine and Atmospheric Science at Stony Brook, tested the utility of coupling a state-of the art atmospheric model with an ocean model from the Stony Brook Storm Surge system to predict storm surges for the New York metropolitan region.

Colle and colleagues tested their combined model against Tropical Storm Floyd and a nor’easter from December 11-12, 1992, and found the model predicted peak water levels comparable to those measured during the storms at several water level gauges around the region.

“Ultimately, the goal is to provide emergency managers with a range of possibilities as to what may happen as the result of a storm, and this approach shows great promise,” says Dr. Colle.

The modelers also performed simulations to assess the impact of parameters such as local tide level and wind intensity on flooding severity.

Model simulations showed that if Tropical Storm Floyd had arrived in New York City a week earlier, coinciding with a spring fortnightly high tide, water levels would likely have been high enough for minor flooding to occur.

Another simulation, which used wind levels of a Category 1 hurricane timed to arrive at spring high tide, predicted water levels likely to have caused significant flooding.

These results suggest that the New York City metropolitan region was spared from flooding during Tropical Storm Floyd only because the storm’s winds had weakened before reaching the region and because the strongest winds luckily occurred during local low tide.

“We’re playing Russian roulette in some sense with these storms coming up the coast,” says Colle. “If we have a high tide or spring high tide when we have one of these events, then we’re in trouble.”

If a category 3 hurricane hit New York City, the U.S. Army Corps of Engineers estimates that nearly 30 percent of the south side of Manhattan would be flooded.

Storm surge flooding could threaten billions of dollars of property and have a grave impact on the lives of the millions of people who live in the city.

During the December 1992 nor’easter, storm tides over-topped some of the region’s seawalls for only a few hours, but managed to flood the NYC subway and the PATH train systems at the train station in Hoboken, New Jersey, shutting by systems down for days.

As sea level rises from the effects of global warming, New York City becomes even more vulnerable to storm surge flooding, the study finds.

It takes high water levels of only 4.92 to 5.74 feet above mean sea level to cause flooding over some of the southern Manhattan Island seawalls.

Meanwhile, global warming is expected to increase the rate at which sea level rises from 0.98 feet per century to 1.64 to 2.46 feet per century.

“The vulnerability of the area speaks for itself as we’ve already had cases of flooding,” says Colle. “When coupled with sea level rise, it’s not going to take much of a storm to cause flooding as we go into the coming decades, so we are working to provide better forecasting of these events in the future.”

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