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Post-tropical storm Sandy: October 2012

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The Background

Millions of homes and businesses were destroyed or damaged by post-tropical storm Sandy earlier this week as it made landfall on the US east coast after sweeping up through the Caribbean.With a full moon on Monday 29 October causing a spring tide, Sandy brought a surge to the Eastern Seaboard that was over 13ft high in some places.

A view from Brooklyn 30 Oct 2012: power outages plunge parts of the skyline into darkness. Photograph © michaelcinquino.com

Insurance impacts

Following an otherwise relatively quiet hurricane season in the US, the financial impact of the storm is still being assessed, but considerable damage has been caused over a wide area due to the exceptionally large wind field and wide range of factors involved.

Damage has been caused by wind, sea surge flooding, flooding from intense rainfall, electrical fires Claims from winter storm damage from snowfall and cold weather as far north as Canada are expected from where the remnant low moved northwards. Snow up to 5ft deep has already been reported in West Virginia.

Insured loss estimates currentlyrange up to $20bn, which would place Sandy among the most expensive hurricanes to have affected the USA. However, these figures remain highly uncertain and estimates will doubtless change as both the damage caused by the storm and the associated policy wordings in insurance contracts are clarified in the coming days. Complexity is expected in relation to policy terms applied to claims, not only because of the complex mix of possible loss causes but also because Sandy was downgraded from a hurricane to a post-tropical storm before it made landfall in New Jersey.

“Frankenstorm": a meteorological monster

Meteorologically, Hurricane Sandy was one of the most extraordinary storms in history. As the eighteenth tropical storm and the tenth hurricane of the 2012 season, it is likely to be one of the largest storms on record at over 1,000 miles across. It was the deepest hurricane to hit the northeast coast of the USA since the Long Island Express Hurricane (also called the New England Hurricane) of 1938.

Tropical storm Sandy developed from an area of low pressure in the Caribbean Sea on Monday 22 October 2012 and was thereafter upgraded to a hurricane on Wednesday 24 October. On the same day, Hurricane Sandy made a first landfall near Kingston, Jamaica, with winds of 80 mph. After crossing Jamaica, Sandy strengthened and on Thursday 25 October made a second landfall in Santiago de Cuba, eastern Cuba, as a category 2 hurricane with winds of 110 mph. While heading through the Bahamas, Sandy briefly weakened to a tropical storm on Saturday 27 October before re-intensifying back up to hurricane strength. Sandy was declared a post-tropical storm shortly before landfall near Atlantic City, New Jersey, at 8pm EDT on Monday 29 October.

As Sandy approached the north-eastern coast of the USA, the warm moist air circulating in the hurricane met cold air spreading south into the north-eastern USA from Canada (a nor’easter storm). This gave the storm additional energy, allowing it to strengthen and produce severe winds, heavy rain and blizzard conditions as it made landfall. The combination of a tropical storm with a passing frontal system is not unusual and is known to potentially increase the intensity of a storm; this is exactly what happened as Sandy approached the coast of the USA.

Sandy rapidly weakened as it headed west across Pennsylvania and was classified as a remnant low on 31 October.

Track map of Sandy from NHC’s running best track (background image: NASA)

Formation and Caribbean

Sandy formed in the Caribbean Sea on 22 October, and was officially upgraded to a hurricane two days later, just before hitting Jamaica. It made second landfall on Cuba the following day as a Category 2 hurricane. That afternoon, the mayor of New York City announced “Zone A” evacuation zones for low-lying areas of NYC as it became clear that Sandy was headed for the north-eastern coast of the USA.

As Sandy started to turn north-west and head for the US coast, the storm surge in Manhattan rose to 13.88ft, more than 3ft higher than the previous record set in 1821. Maximum sustained wind speeds were 90mph by late Monday morning and the NY borough of Queens was underwater. New Jersey, already heavily flooded, was set to bear the brunt of Sandy’s arrival, but the effects of the storm were already evident in Maryland, Delaware, and other nearby states. In Rhode Island, the storm surge reached 6ft while still two hours before high tide.

Western Atlantic journey

As Sandy swept out of the Caribbean, by then Category 1, a state of emergency was declared first in New York, then in New Jersey, with NYC public transport shutting down from Sunday evening ahead of the hurricane’s predicted landfall on Monday. By that time, Sandy was 940 miles across, by far the largest windstorm on record to have hit the region.

Landfall and journey over land

By 7pm, Sandy was reclassified to a Category 1 post-tropical cyclone. It made landfall minutes later near Atlantic City, NJ. Many parts of New Jersey were by that time underwater and damaged or destroyed, including the Atlantic City casinos and famous boardwalk. The last tunnel out of Manhattan was closed just over an hour later, as tunnels and subways began to be infiltrated with floodwaters. Flooding went on spreading through the night as Sandy continued north-west. Breezy Point, in the NY borough of Queens, caught ablaze with an electrical fire that eventually destroyed around 100 homes. 7.4 million homes awoke on Tuesday without power and NJ governor Chris Christie described the Jersey Shore damage as “unthinkable”. Hundreds of miles from Sandy’s devastating centre, Chicago surfers were reported to be riding the 20ft-high waves generated on Lake Michigan by the storm.

The image of the damage

Twitter user, Raven Chiara, @ravenchiara tweeted this picture of Hoboken, NJ, - completely underwater

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