Hurricane Sandy, USA, 2012

A late-season hurricane meeting a winter system

Sandy formed over warm Caribbean water in late October, unusually late in the hurricane season. As it moved north it merged with a cold winter weather system, which fed it fresh energy and stretched its wind field until the storm was nearly a thousand miles across, spreading surge and gales over a huge length of coastline.

A track bent into the coast

A blocking ridge of high pressure near Greenland stopped Sandy curving out to sea, the path most late-season storms take. Instead the storm was steered sharply west into New Jersey. This rare track put New York and the most densely built stretch of the US coast on the strongest side of the storm.

A surge arriving at high tide

Sandy's landfall coincided almost exactly with a spring high tide under a full moon. The surge stacked on top of already high water, lifting the sea at The Battery to 9.4 feet above normal. That extra timing, as much as the storm's strength, is what pushed the ocean over defences and into the city.

A crowded, low-lying coastline

More than 1 million people, along with subways, road tunnels, airports and power substations, sit within a few metres of sea level in New York and along the New Jersey shore. Decades of building on barrier islands and reclaimed waterfront put enormous value directly in the path of any storm surge.

Primary

• A storm surge of 9.4 feet above normal tide flooded lower Manhattan and long stretches of the New Jersey coast.
• Winds near 80 mph brought down trees and power lines across several states.
• Heavy snow fell inland across the Appalachians, with a peak storm total of 36 inches near Richwood in West Virginia.

Secondary

• Storm surge flooded eight of the MTA's tunnels, and subway service between Manhattan and Brooklyn was out for weeks.
• About 8.5 million customers, homes and businesses alike, lost electricity, some for more than two weeks.
• A fire in the flooded Breezy Point district of Queens destroyed at least 100 homes.
• Petrol shortages followed as flooded terminals and power cuts closed filling stations.

Social

• Sandy caused 72 direct deaths in the mid-Atlantic and northeastern United States, many by drowning in the surge.
• Thousands of homes on the New Jersey shore and in districts such as Staten Island were left uninhabitable.
• Hospitals, including NYU Langone in Manhattan, had to evacuate patients when backup power failed.

Economic

• Damage in the USA came to about 71 billion dollars, then second only to Hurricane Katrina.
• The New York Stock Exchange closed for two days, its first two-day weather closure since the nineteenth century.
• Transport, businesses and tourism lost billions more during weeks of disruption.

Environmental

• Salt water contaminated wetlands, parks and groundwater near the coast.
• Beaches and protective dunes along the New Jersey shore were stripped away.
• Raw sewage overflowed into waterways when treatment plants flooded.

Immediate

• Around 375,000 people in low-lying zones of New York City were ordered to evacuate before landfall.
• The subway, schools and airports were shut in advance and emergency shelters opened.
• FEMA and the National Guard delivered food, water and fuel, and utility crews arrived from across the country.
• The federal government declared major disasters in the worst hit states, releasing emergency funding.

Long term

• Congress approved an aid package of around 50 billion dollars for rebuilding.
• New York invested in resilience, hardening the subway, raising electrical equipment and building flood defences.
• The Rebuild by Design competition funded schemes such as the Big U flood barrier around lower Manhattan.
• Thousands of damaged homes in flood-prone areas such as Staten Island were bought out and returned to open land.