Across the eastern US, Americans made frantic preparations Saturday for a possible superstorm as Hurricane Sandy lumbered north after leaving 59 people dead in the Caribbean.

The so-called "Frankenstorm" was expected to make landfall somewhere between Virginia and Massachusetts early Tuesday, hitting during the frenzied final week of campaigning before the US elections on November 6.

The storm was at category one hurricane strength at 1800 GMT, with sustained winds of 75 miles (120 kilometers) per hour as it moved along the east coast, the National Hurricane Center said.

"Sandy (is) producing tropical storm-force winds over the Atlantic from the northern Bahamas to near the coast of North Carolina," the center said, adding that the storm was traveling in a northeasterly direction at 11 miles (18 kilometers) per hour.

Forecasters at the National Weather Service warned the storm would "result in significant impacts along coastal North Carolina" beginning late Saturday.

Sandy could cause "moderate coastal flooding and rough surf" through Monday, drenching the state with three to five inches (seven to 13 centimeters) of rain inland and as much as five to eight inches along the coast, they warned.

But forecasters and emergency officials were far more worried about what could happen further north.

"This is a large storm that is forecasted to impact the Mid-Atlantic and other parts of the East Coast with strong winds, coastal flooding, inland flooding, rain and snow," said Craig Fugate, head of the US Federal Emergency Management Agency.

"People should be ready for the possibility of power outages paired with cold temperatures," he said in a statement Saturday.

Sandy's likely collision early next week with a seasonal "nor'easter" weather system was predicted to super-charge the storm, dragging it to the west where it is expected to slam into the coastal US states of Virginia, West Virginia, Pennsylvania, New York, New Jersey, Connecticut, Massachusetts and even inland Ohio.

Alex Sosnowski, an expert senior meteorologist for Accuweather.com, called Sandy "an extremely rare and dangerous storm," menacing 60 million people, that "could lead to billions of dollars in damage."

Residents were bracing for huge tidal surges, power outages, inland flooding and even heavy snowfall on high ground far from the coast.

"Sandy will be more like a large nor'easter on steroids," Sosnowski wrote.

It could have the strength of a category one or two hurricane, he explained, but with powerful winds extending out hundreds of miles from the center.

President Barack Obama was briefed by top emergency officials Saturday, the White House said, and governors declared states of emergency in Maryland, New York, New Jersey, Connecticut, Pennsylvania, Virginia, the US capital Washington and a coastal county in North Carolina.

The mayor of New York, Michael Bloomberg, said the Big Apple was ready for anything Sandy could throw at it, and cautioned against panic.

"Whenever we're faced with a tough situation, New Yorkers always show courage, compassion, and presence of mind #Sandy," he tweeted.

The storm was a hot topic on Twitter, with people sharing fears and bluster, or just trading stories of stocking up.

"$30 flashlights. What is the world coming to? #Sandy," wrote Lisa Brock, in New York City.

Meanwhile, concern was also mounting that storm damage and power outages could have a major impact on voter turnout, polling station readiness and last-minute campaigning by Obama and his Republican rival Mitt Romney.

US Vice President Joe Biden canceled a Saturday appearance in Virginia Beach to allow officials to focus on storm preparations and Romney did the same.

White House spokesman Josh Earnest told reporters Saturday the president was giving priority to preparations for the impending storm over campaigning, but had not so far changed his schedule because of Sandy.

Meteorologists have nicknamed the unusual confluence of weather patterns a "Frankenstorm," because it is due to hit just before Halloween on October 31 and is composed of parts from different sources, as was Frankenstein's monster.

The powerful hurricane earlier claimed 11 lives in eastern Cuba, including several people who died in the rubble of collapsed buildings.

On Wednesday, Sandy unleashed its wrath on Jamaica, where one person died, and on Haiti, where 44 people were killed according to an updated official toll.

Two people were reported dead in the Dominican Republic and one in the Bahamas.

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