Buffeting Manhattan with screeching winds that gusted up to 90 miles per hour, the Nor’Easter of 1992 roiled the waters, creating a storm surge that pushed the sea over New York’s shores and into the network of tunnels under the city. Winds whipped up waves already on top of the especially high tide of a full moon, causing the water to rise almost eight feet above sea level. It inundated parts of downtown Manhattan under four feet of water and flooded a Con Ed station, cutting off electrical power and shutting down the entire subway system, parts of it for 10 days. The storm flooded LaGuardia’s runways, grounding the planes. It swamped train tracks on all the commuter railroads, submerged cars on the FDR Drive under four and a half feet of water, flooded the Battery Tunnel and caused the cancellation of all ferries and the closing of city bridges. People stranded in their cars and in a stalled train in the PATH tunnel had to be rescued by emergency workers. The storm’s fury pummeled the city for almost three days.
Sandy is threatening New York City with a similar scenario. Hurricanes are not new to the East coast and New York, but Hurricane Sandy is forecast to be the mother of all them. Here’s why:
Every possible factor that increases the destructive power of a storm is present— storm surge, timing: high tide, full moon; position: northeast quadrant; wind and rain. Sandy is the largest hurricane on record— 1,000 miles across— and is about to join forces with two weather conditions that will intensify it and extend its duration. A low-pressure trough coming from the west will supply a great deal more energy. There is also a high-pressure zone that is over Greenland and will block the hurricane from blowing away over the ocean. The longer it stays in place, the more damage it will cause.
Storm surge, what hurricane expert Max Mayfield calls a “large dome of water, often as wide as 50 miles across, that comes sweeping across the coastline,” is the hurricane’s greatest danger. Wind-driven waves increase the height of the wall of water to 15 feet or more above the usual water level. Predictions are that Sandy’s surge will be six to 12 feet in NYC.
Timing is important. The waters rise higher when a storm surge occurs at high tide. A full moon will raise the wall even more. Sandy will slam into New York at precisely the time of the high tide when the moon is full, and waves of four to eight feet are predicted on top of the six to 12-foot surge. If these predictions are accurate, a wall of water, 10 feet high at a minimum, will easily top the three-foot barrier at Battery Park City.
Position New York will be in the path of the northeast quadrant, the most destructive area of the storm. A hurricane spins counter-clockwise. Imagine the northeast quadrant at two o’clock on the face of a watch. Sandy comes from the south (six o’clock), picking up water and wind. It slams first into the northeast quadrant at its most intense and weakens as it goes inland.
New York City’s geography seems designed for maximum risk. Four of the city’s five boroughs are islands, with 578 miles of exposed coastline. New York harbor, and behind it Manhattan, are at the apex of a triangle formed by Long Island and the Jersey coastline. Because Long Island is almost perpendicular to New Jersey, this near right angle would tend to funnel the surge of a hurricane striking, like Sandy, a little west of the city, through the Narrows into New York harbor and from there straight ahead to Manhattan. The gentle slope of the wide continental shelf off the coast of NY harbor facilitates the forward movement of the surge, adding a third dimension to the triangle. Long Island Sound’s east-west orientation funnels the hurricane’s winds along the Sound to the upper East River.
Much of the city is at a low elevation— in Manhattan, the financial district, Battery Park, South Street Seaport area, and the lower West Side from the Battery to Midtown are the most susceptible to flooding. The airports are in low-lying areas, and much of the city’s crucial infrastructure— power and telecommunications grids, subways, sewers, rail tunnels— are underground. Even on a dry day, reported the Wall Street Journal in 2009, the subway pumps out 14 million gallons of groundwater from its tunnels.
Sandy’s winds will gust to 60-80 mph, driving its two to four inches of rain and adding to the flooding caused by the surge and the waves.
And if all that weren’t enough, global warming plays a role too. Sea level rise is due mostly to the warming of the world’s oceans and melting mountain glaciers. The sea level has crept steadily upward throughout the 20th century and has accelerated since the 1990’s.
According to a 2008 study of 136 port cities around the world by the international Office of Economic Cooperation and Development, New York ranks in the top 10 of the world’s major coastal cities with the highest potential of loss from coastal flooding. With eight million people, billions of dollars of real estate and a financial center of worldwide importance, a catastrophic hit to New York would trigger global losses as well. The OECD estimated that New York-Newark have an estimated 2.15 trillion dollars of threatened assets. Rising sea levels and the predicted increased frequency and intensity of major storms, both consequences of global warming, augment the potential for disaster posed by New York City’s unique geography, coastline erosion and loss of wetlands, all of which greatly increase the probability of flooding.