What made Hurricane Sandy’s impact so great?
A week after hitting the Caribbean, Hurricane Sandy made landfall along the east coast of the US on Monday evening as a powerful storm.
Worst fears have been realised, with 16 people killed, millions of homes without power, and road, rail and airline networks paralysed.
Only last year, New York City and other parts of the eastern US were hit by Hurricane Irene, which left a trail of damage and disruption, estimated by NOAA to have cost $19bn.
So what has made Hurricane Sandy’s impact so great?
The size of Hurricane Sandy was truly phenomenal – something that can only be fully appreciated when looking at the storm on a satellite picture.
Prior to making landfall, hurricane-force winds (sustained speed of 74mph and above) and tropical storm-force winds (sustained speed of 39-73mph) extended 175 miles and 485 miles from the centre of the storm respectively.
According to NOAA, in a typical large hurricane, tropical storm-force winds would only reach out 300 miles from a storm’s centre.
To put this into context, if the centre of hurricane Sandy was placed over Paris, the tropical-storm force winds would affect much of western Europe – as shown by the green circle on the map below.
Sandy’s track has been crucial in terms of the impact that it has had. Normally, hurricanes that move along the east coast of the US are steered out across the Atlantic Ocean by the west to east movement of the jet stream.
However, on this occasion, the jet stream was taking a more north to south track, having less of a steering effect on Sandy.
In addition, there was a big area of high pressure to the north east of the US which effectively blocked Sandy from moving out into the Atlantic. As a result, the storm was forced to take a left turn, slamming into the east coast.
Not only is this an unusual route for a hurricane to take, it is a route that put around 60 million people in its path.
Storm surge and high tide
As the storm made landfall, there was a major storm surge along coastal areas on its northern side caused by onshore hurricane-force winds pushing water onto the coastline.
Also, with a full moon, high tides were occurring, which only added to the water levels along the shore.
These factors combined to cause major coastal flooding – especially for low-lying areas. Battery Park, New York City had storm surges reaching a record-breaking 14ft, sending torrents of water into lower Manhattan.
Hurricane-force winds lashed the coastline from New Jersey to Massachusetts where gusts of up to 90mph were experienced.
This strength of wind came at a time of year when some trees are still in leaf. Leaves on trees act as sails and make them more prone to being blown down, as does heavy rain, softening the ground that holds their roots.
Urban areas are even more prone to damage from strong winds because the layout of buildings can cause the wind to funnel between them, giving the wind an extra kick.
Very tall buildings like skyscrapers would have experienced even stronger winds than those measured at ground level. This is because the wind blows even faster just a few hundred metres above the ground due to it experiencing less friction and flowing more freely.
It is probable that the top of the Empire State building experienced wind gusts in the range of 120mph, if not a little more.
There’s no doubt that some will debate on whether climate change can be said to have had an influence on hurricane Sandy. However, it’s not wise or reasonable to use a single weather event when considering a changing climate.
On the other hand, future predictions of a warmer world would allow the atmosphere to hold more moisture, which could equate to more significant rainfall events taking place.
Also, warmer ocean waters could potentially give hurricanes a bigger playground in which to roam, as this is where they draw their energy from in order to thrive.
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