The amount of damage the East Coast is going to absorb is hard to estimate because the storm's track is in a state of flux, said Tom Larsen, senior vice president and product architect at Eqecat Inc., a risk modeler in Oakland, Calif.
Larsen said he doesn't expect Sandy to be worse than Irene, which struck the East Coast in August 2011, killing at least 45 people and causing at least $15.8 billion in damage, according to the hurricane center.
"Right now, in terms of loss levels, Irene is the best kind of guideline," Larsen said. "It doesn't look to be a whole lot worse than Irene."
Because weather models keep changing, Sandy's official track will change as well, Downs said. The hurricane center warns that tracks are just estimates and subject to change.
"Regardless of the exact track of Sandy, it is likely that significant impacts will be felt over portions of the U.S. East Coast through the weekend into early next week," Michael Brennan, a senior hurricane specialist at the center in Miami, said in a forecast analysis.
The storm may hit anywhere from the mid-Atlantic states starting Oct. 28 to southern New England later in the week, said Gary Best, a meteorologist for Hometown Forecast Services Inc. in Nashua, New Hampshire.
"A very complicated situation is going on right now," Best said by telephone. "As it moves across the western Atlantic, it is going to encounter a dip in the jet stream. There will be a lot of energy coming in from the West and it may try to capture the storm and pull it into the U.S. coastline."
New York City has a 55 percent chance of winds of at least 39 mph by Oct. 30, according to estimates by Tropical Storm Risk, a consortium of experts on insurance, risk management and climate supported by the British government.
Cold air over the Appalachian Mountains may mix with the moisture and drop several inches of snow, Best said. The cities along the East Coast will probably have rain.
— With assistance from Jim Polson and Henry Goldman in New York, Lynn Doan in San Francisco, Yee Kai Pin in Singapore and Julie Johnsson in Chicago.