CNN - Hurricane Sandy is a wolf in sheep's skin poised to assail New England at the beginning of next week, with the potential to cause widespread damage in the highly populated area.
It is losing wind speed but is huge and likely to merge with a winter storm front and turn into a "Frankenstorm" over the northeastern United States just before Halloween, according to the National Weather Service.
Sandy has already left at least 21 dead, as it ground over Haiti, Jamaica and Cuba.
It weakened to a category one hurricane late Thursday and could drop down to a tropical storm before rolling onto land somewhere between Virginia and Massachusetts, says the National Weather Service. But it warns the storm "could become a menace to the Northeast."
Local news weather forecasters in Philadelphia are warning viewers that Sandy could be a storm of historical proportions and that the City of Brotherly Love could take a direct hit.
Residents in South Jersey have already begun stocking up on batteries and bottled water, and hardware stores have put up preparedness displays, CNN affiliate WKYW reported. One location quickly sold out of electric generators.
With a cloud field spanning over 1,600 miles, Sandy is massive, says CNN meteorologist PedramJavaheri. That's about the distance from Memphis to Los Angeles as the crow flies.
"Sandy should continue to expand in size," according to an NWS advisory at 11 p.m. Thursday.
There is a 90% chance it will hit the American Northeast, Javaheri said, where a billion dollars in damage could mount as it rolls inland as far as the Midwest.
Even if it weakens, its gale force winds could still reach 60 mph, toppling trees still laden with leaves, which makes them heavier and more susceptible to wind, according to CNN affiliate WKYW in Philadelphia, but that is not the major concern.
With the load of moisture it is carrying, it is expected to dump six to eight -- and maybe even ten inches -- of rain in the hardest hit coastal regions, WKYW reported.
As Sandy turns landward in the coming days, it may be met by a winter storm front crawling to the east out of U.S. heartland. They could collide and join, producing an even larger, stronger storm.
CNN's Ed Payne contributed to this report