Soon after superstorm Sandy struck New York and New Jersey a year ago today, the public became aware that a half-dozen U.S. weather models had incorrectly predicted that the storm coming up the coast would veer northeast out to sea. Only the so-called European model predicted that Sandy would “turn left” and threaten the coast of the nation’s most populous city and the surrounding metropolitan area. Less was heard about another set of models that had attempted to predict how high the storm surge would be, a rough guide to how much coastal land might be flooded. The best forecasts gave a wide range: six to 11 feet.
Needless to say, an 11-foot flood is a lot different than a six-foot flood. And any surge varies in height locally over many miles of coastline. Scientists are now using data about Sandy to try to create forecasts that can better define impending surges, and can help urban planners and engineers figure out what kinds of barriers might reduce future flooding.
One of those scientists is Philip Orton, an ocean engineer at Stevens Institute of Technology in Hoboken, N.J., a city of about 50,000 people, in the New York City metropolitan area, that Sandy swamped under eight feet of salt water. He and his colleagues have taken the storm’s physics apart to try to understand it. “We get so few hurricanes here in the Northeast,” Orton says. “Sandy is a great opportunity.”
Basically, Orton and his colleagues separated the different factors that can cause ocean water to rise, such as changes in atmospheric pressure, wind direction, tides, swelling rivers pouring into the sea. They then modeled the factors individually and wove them back together to experiment with changes to each parameter. Among the results were animations that recreated and accurately described Sandy’s flooding; two of them can be seen below.
Wind and pressure build storm surge. Winds (arrows) blowing in from the northeast across the Atlantic Ocean during the days preceding Sandy’s landfall started to pile water up against the mid-Atlantic coast. As Sandy itself approached, atmospheric pressure (black lines) gradients from high-pressure areas around the storm to the low-pressure center cause water to rise under the storm, where the pressure is much lower. The animation runs from late October 26 through Sandy’s peak surge onto land at about 10 p.m. on October 29, and beyond. The large image shows storm surge across the region, mapped onto longitude and latitude. The inset graph shows the surge height (in meters) at the shore in Sandy Hook, N.J., next to Manhattan, and color on the map shows surge height region-wide (scale bar at far right). Tidal information is not included.
Orton’s team is preparing a paper on the results, and is already comparing notes with other groups that model storms, including the Dutch company Arcadis and the U.S. National Hurricane Center. The center provides warnings that give a range of possible surge heights across local regions, but the new insights could lead to models that can predict flooding more specifically, “neighborhood by neighborhood” Orton hopes. That kind of detail could help authorities decide where to order evacuations when a big storm hits.
In the future, Orton says, improved storm-surge models could predict where flood zones should be drawn given future sea level rise, which is now done nationally by the Federal Emergency Management Agency with data from past storms. The models could also predict whether expanded wetlands, or shallower channels into bays and estuaries, could reduce surges—an analysis underway for the large and tattered Jamaica Bay that borders a long section of Queens and Brooklyn, two New York City boroughs that Sandy damaged heavily.
The models could also be used to assess whether enormous manmade barriers outside various major cities would hold back water, and if they would make flooding worse in neighborhoods adjacent to the structures. In particular, that kind of work could help scientists, engineers and government officials decide whether to build a controversial Outer Harbor Gateway barrier that would link Queens with New Jersey to keep storm surges out of the greater New York metropolitan area.
How Hoboken flooded. Sandy hit at night, making it hard to see the entry points of floodwaters into neighborhoods. This animation shows where water entered Hoboken, N.J., on the west side of the Hudson River right across from Manhattan, how it flowed across the land and how deep it became. Watching the animation slowly and carefully could give strong clues about where to build barriers that could prevent future flooding. Sandy’s surge entered the city through only a few hundred meters of shoreline, visible at the top and bottom of the image on the evening of October 29 (between 29/12 and 30/00). Water depth in the city is shown at the bar on the right (in feet). The elevation of the Hudson River’s water next to Hoboken is shown across the bottom, over time (October date/hour of day).