Experts take to the air to study storm damage

National Weather Service experts flew in an NYPD helicopter and made an aerial survey of two areas of the city ravaged by Thursday's storm as they try to decide if a tornado caused the massive damage and one fatality, officials said.

Weather experts will also be making visits on the ground to study patterns of wind damage which are the main clues for determining if a storm had become a tornado, the officials said. As of 4 p.m., the agency expected to have team in Prospect Park shortly.

More than 900 trees were felled in a swath that stretches from Park Slope in Brooklyn to Bayside, Queens. One tree struck and killed a woman riding in a car on the Grand Central Parkway. A determination of what kind of storm hit the city could take until Saturday, weather experts said.

Telltale clues being studied are patterns of the fallen trees, which meteorologist George Wright of Manhattan said are reliable indicators of a tornado.

"One of the things you look for is a rotational signature, whether it is crops or trees," said Wright. "Thunderstorms produce straight line wind damage . . . a tornado will take trees and rotate them in circular pattern which indicates rotation."

Wright said that Doppler radar images from Thursday showed rotational winds. But while rotations can develop into a funnel cloud they aren't classified as a tornado until the funnel touches the ground, explained Wright.

But even straight line winds from a downward-rushing microburst can reach as high as 120 miles an hour, said consulting meteorologist Thomas Piazza of Chicago. Wright said there were reports of 122 mile-an-hour winds in Bayonne, N.J.

Forecasters said a small tornado did touch down in southern New Jersey, knocking over trees and damaging two houses.

Eight twisters have hit New York City since 1950, the weather service said. The last was in July, a small one that whirled through the Bronx during a thunderstorm that left thousands without power. In 2007, a tornado with winds as high as 135 mph touched down in Staten Island and Brooklyn, where it damaged homes and sucked the roof off a car dealership.

With AP