Sandy was expected to move past the Bahamas by Friday evening and head north off the US coast.

Forecasters say Sandy is expected to be pulled in by another storm system moving from the west, making it come ashore in the northeastern United States late Monday or early Tuesday and  unleashing heavy rains, storm surges and possibly near hurricane-force winds.

Weather trackers say the hardest-hit areas could span anywhere from the coastal Carolinas up to Maine, with New York City and the Boston area potentially in harm's way.

"There are many questions surrounding this hurricane and its forecast, but I find it important to convey that Sandy's impacts will be widespread, no matter the location of landfall," Jeff Masters, a hurricane expert at private forecaster Weather Underground (www.wundergournd.com), wrote in a blog.

He said a landfall by Sandy along the Mid-Atlantic coast could trigger "a billion-dollar disaster."

Residents of Kingston try to cross the Hope River after a bridge was washed out by Hurricane Sandy in Kingston, the capital City of Jamaica, Oct 25, 2012. [Photo/Agencies]

Amid final preparations for the crucial Nov 6 US presidential election, the storm could hit an area of New England where Hurricane Irene caused severe damage last year.

Unlike Irene, which caused billions of dollars in damage as it battered the Northeast in August last year, Sandy is forecast to be a weaker storm but will be moving slower than Irene, likely bringing more rain and increasing its potential for damage, weather forecasters said.

At $4.3 billion in losses, Irene ranks as one of the ten costliest hurricanes, adjusted for inflation and excluding federally insured damage, according to the Insurance Information Institute, an industry group.

Sandy is expected to hit the United States during a full moon, increasing the flood potential since tides will be at or near their highest.