"We don't have many modern precedents for what the models are suggesting," Cisco said.
It is likely to hit during a full moon when tides are near their highest, increasing coastal flooding potential, NOAA forecasts warn. And with some trees still leafy and the potential for snow, power outages could last to Election Day, some meteorologists fear.
Some have compared it to the so-called Perfect Storm that struck off the coast of New England in 1991, but Cisco said that one didn't hit as populated an area and is not comparable to what the East Coast may be facing. Nor is it like last year's Halloween storm, which was merely an early snowstorm in the Northeast.
"The Perfect Storm only did $200 million of damage and I'm thinking a billion," said Jeff Masters, meteorology director of the private service Weather Underground. "Yeah, it will be worse."
But this is several days in advance, when weather forecasts are usually far less accurate. The National Hurricane Center only predicts five days in advance, and each long-range forecast moves Sandy's track closer to the coast early next week. The latest has the storm just off central New Jersey's shore at 8 a.m. on Tuesday.
As forecasts became more focused Thursday, the chance of the storm bypassing much of the coast and coming ashore in Maine faded, Cisco said.
The hurricane center's Franklin called it "a big mess for an awful lot of people in the early part of next week."
Associated Press writer Tony Winton contributed to this report from Miami.
NOAA's Hydrometeorological Prediction Center: http://www.hpc.ncep.noaa.gov/index.shtml
National Hurricane Center: http://www.nhc.noaa.gov/
Seth Borenstein can be followed at http://twitter.com/borenbears