A European computer model saw Sandy's sharp left turn nearly eight days early
On October 23, 2012, a forecast from the European Centre for Medium-Range Weather Forecasts in Reading, England, predicted something unusual. Instead of curving out to sea, Hurricane Sandy would swing west and hit New York and New Jersey on October 29. American forecasters confirmed that path only four days later.
Most Atlantic hurricanes heading north are shoved east by the prevailing westerly winds. In late October 2012 a ridge of high pressure over Greenland blocked that pattern and bent the jet stream back on itself off the East Coast. Sandy was drawn into the resulting flow and driven on a rare north-westward track, merging along the way with a stalled Arctic front. Scientists disagreed on the cause: one writer linked the odd jet stream to melting Arctic ice, while the climatologist Kevin Trenberth said natural variability remained the default explanation, adding that all weather now unfolds in a warmer, moister environment.
The storm grew enormous. By October 29 its tropical-storm-force winds spanned about 1,150 miles, the widest Atlantic hurricane on record, and its central pressure of 940 millibars set low-pressure records for many north-eastern cities. It had stopped being a tropical system shortly before it came ashore close to Brigantine, New Jersey, still carrying sustained 80 mph winds, and its surge flooded New York City's streets, tunnels and subway lines. A sea level roughly 30 centimetres higher than a century earlier added to the flooding.
The toll was vast: 254 deaths across eight countries and nearly 70 billion US dollars in damage, including 65 billion in the United States, where 24 states were affected. Earlier, in Jamaica, winds cut power to 70 per cent of residents, and flooding from its outer bands killed 75 people in Haiti.
The episode stung American meteorology. The National Weather Service was criticised for not using higher-resolution models as the European centre did, and an upgrade finished at the end of 2013 improved its forecasts.
Source: Hurricane Sandy
