Any city would suffer if 500 million tons of seawater were to spin ashore at a hundred miles (160 kilometers) per hour. But it turns out New York City—which the remnants of Hurricane Sandy hit hard this week—suffers more than most.

“Whenever a hurricane comes up here,” said Nicholas Coch, a professor of sedimentology and coastal geology at Queens College, “you add one to the category because we’re in the worst possible place in the world to be.”

Indeed as New Yorkers saw, it only takes a Category 1 hurricane to cause a massive flood of subways, car tunnels, streets, and airports. Let’s take a look at why New York is so vulnerable.

Reason #1: The “New York Bight”

A “bight” is a curve or bend on an open shoreline. Think of the Bight of Australia, that wide, upside-down U on the bottom of the continent, or the Bight of Benin on the western coast of Africa, which pockets a portion of the Atlantic Ocean stretching 400 miles (640 kilometers) eastward from Ghana to the outlet of the Niger River.

On the other side of the Atlantic, there’s the New York Bight, where Long Island and New Jersey form an upside-down L around shallow waters of the Atlantic Ocean.

When Hurricane Sandy arrived at the New York Bight, it brought all the millions of tons of ocean water and rain it accumulated on its way up the coast.

When all of this water slammed into New York’s Bight, the water got trapped where the legs of the L form. With nowhere to go, water then spilled onto the land, including the southernmost point of New York City, where the New York Stock Exchange and the Statue of Liberty stand. Waves from this excess water piled up and formed storm surges of dangerous height.

This phenomenon is only worsened if surrounding waters are shallow, as they are all around New York City. The shallower the waters, the deeper the surge (think about a short empty cup, versus a tall empty cup, if you pour the same amount of water in both cups, the shorter cup will overflow).

A typical Category 1 hurricane like Sandy produces a storm surge of three to five feet (0.9 to 1.5 meters). That was the effect when Hurricane Gaston struck South Carolina in 2004. Around 8 p.m. ET Monday, Hurricane Sandy hit the Jersey coast at 90 miles (145 kilometers) per hour and spun into New York City.

Water levels in the city’s financial district reached a record 13.88 feet (4.2 meters), the highest the area has seen since the hurricane of 1821, which only brought 11.2 feet (3.4 meters) of water ashore.

Reason #2: High buildings and bridges are highly vulnerable.

With a huge storm like Sandy, high winds can arrive before the hurricane actually hits, and the higher you go, the earlier you feel those winds. And New York City’s 5,818 completed high rises make it the second tallest city in the world after Hong Kong.

Sandy’s wind began whistling through the city four days before the storm hit. If you live on a higher floor, your windows may blow off entirely, as happened in a JP Morgan office building.

A typical Category 3 hurricane will bring winds to the ground three to four hours before making landfall in New York City. Add 150 to 200 feet (46 to 60 meters) to your altitude and you can detect hurricane winds up to six hours before the storm hits the ground.

The many suspension bridges in New York add to the city’s wind vulnerability. City officials began cutting off access to all bridges before 7 p.m. on Monday, from the Brooklyn Bridge in the east to the Verrazano and George Washington bridges, lest the bridges collapse in the wind.

Reason #3: New York has many vital underground systems that are prone to flooding.

Beneath the city is one of the most impressive municipal water systems in the world, the subway, and car tunnels. When Hurricane Sandy made landfall and water filled Lower Manhattan, anything underground was immediately flooded.

Water filled all of the subway tunnels, including the 4,000-foot Brooklyn Battery Tunnel, as well as the four tunnels that cars use to go in and out of the city. The flooded water is saltwater from the ocean, which corrodes the city’s aging pipes and subway tracks.

Reason #4: The edge of the city is full of vital facilities.

There are ten emergency service stations, 19 colleges, nearly 500 schools, 23 hospitals, 57 nursing homes, 17 power plants, and 13 wastewater treatment plants located along the coast of New York City.

Also on the Manhattan coast is the financial district where Wall Street and the New York Stock Exchange are located, which means New York’s extra hurricane vulnerability isn’t just a problem for the Big Apple but for the world’s financial community as well.