Gary Strauss and Doyle Rice, USA TODAY
Sandy -- dubbed "Frankenstorm" for its potential monstrous effects -- has millions bracing for a massive weather system likely to drench much of the Eastern seaboard by Monday.

For the 50 million people who live in the Mid-Atlantic and Northeast - roughly one-sixth of the U.S. population - the storm's winds, rains and potential snow could cause widespread havoc, with weather forecasters predicting up to 10 inches of rain in some regions, snowstorms in others and widespread wind damage that could down power lines.

At least 43 deaths in Cuba, Jamaica and Haiti were already reported in Sandy's wake, including a 4-month-old Cuban boy crushed when his home collapsed. There were no reports of injuries at the U.S. naval base at Guantanamo Bay.

After briefly weakening to a tropical storm overnight, Sandy re-strengthened into a hurricane this morning, the National Hurricane Center reports.

As of 8 a.m., the center of Hurricane Sandy was located about miles southeast of Charleston, S.C. Sandy now has a sustained wind speed of 75 mph and is moving to the north-northeast at about 10 mph.

It is a massive storm, with tropical storm force winds that extend outward up to 450 miles from its center.

All of the computer models that meteorologists use to forecast weather show Sandy turning left off North Carolina and heading back toward the mid-Atlantic coast. The latest track forecast from the hurricane center shows the center of Sandy making landfall in southern New Jersey late Monday.

"This will be a long-lasting event, with two to three days of impact," said James Franklin, branch chief of the National Hurricane Center. "Wind damage, widespread power outages, inland flooding and storm surge are all likely."

Sandy is gearing up for an assault from South Carolina to New England. Weather forecasters said the storm will likely run into a cold front approaching from the Midwest, which could dump up to two feet of snow in parts of West Virginia and Virginia.

"This is a very unusual weather event as a result of a late season hurricane combining with cold front from the West,'' said Virginia Gov. Robert McDonnell, who declared a state emergency Friday in advance of the storm to aid disaster preparations. "This is still an unpredictable weather event, but one that's possibly very dangerous."

In the final weeks before the U.S. presidential election on November 6, the storm was presenting a challenge to the campaigns of President Obama and his Republican challenger Mitt Romney.

Romney cancelled a rally scheduled for Sunday evening in Virginia Beach, Virginia, while President Obama's re-election campaign announced that Vice President Joe Biden had also cancelled a Saturday trip to Virginia Beach.

Early Saturday, Sandy was about 155 miles north of Great Abaco Island in the Bahamas, and about 350 miles south-southeast of Charleston, S.C. Its sustained wind speed dropped below 70 mph, which downgraded the storm from hurricane strength.

"We are now 90% certain the storm will make landfall in the U.S.," said Louis Uccellini, director of NOAA's National Centers for Environmental Prediction.

AccuWeather meteorologist Tom Kines says winds could have the biggest impact, causing widespread power outages. "You've got to be concerned since it's an area with such a large population," Kines says.

Delaware was bracing for a threat rivaling the March 1962 nor'easter that has stood as the state's worst storm. Delaware's top environmental officer, Dept. Natural Resources and Environmental Control Sec. Collin O'Mara, said Sandy could unleash record waves and tidal flooding along the coast."The potential on this is greater than the defenses that we have in mostplaces," O'Mara said. "We're taking this as an extremely significant problem,probably the most-significant we've seen in decades. We're taking every possible precaution."

Insurer Allstate was expanding efforts to prepare for the storm, spokeswoman April Eaton said."We are currently rolling our catastrophe personnel, mobile claim centers and catastrophe response vehicles to Raleigh, N.C., for staging," she said. "Staging allows us to get our national catastrophe team members and units positioned in a safe place, but close to areas that may be impacted by Sandy. Once we see where the hurricane makes landfall, and authorities allow us in, we're able to move from the staging area or holding pattern and go into the heavily damaged communities to help Allstate customers begin the claim process."Eaton said they plan to send nine mobile claim centers to Raleigh, N.C., and Allentown, Pa.

Florida Power & Light officials reported as many as 8,500 customers in Brevard County lost power Friday. About 400 customers remained without power about 10 p.m.

The National Hurricane Center issued a tropical storm warning as far north in Florida as St. Augustine and parts of North and South Carolina.

Tropical storm warnings were issued for parts of Florida's East Coast, along with parts of coastal North and South Carolina and the Bahamas. Tropical storm watches were issued for coastal Georgia and parts of South Carolina, along with parts of Florida and Bermuda.

Florida officials say they don't expect flooding, but have warned residents to stock up on supplies and be prepared for several days without power.

"We encourage people to have enough food, water, medicines, flashlights and batteries -- things to take care of yourself for at least 72 hours," said Bryan Koon, director of Florida's Division of Emergency Management.

Power outages could last for days, Weather Channel meteorologist Chris Dolce says, and there could be just enough cold air to produce wet snow, possibly heavy, in some parts of the central Appalachian mountains of West Virginia and Pennsylvania.

Pepco, the electric company that provides service to Washington, D.C., and parts of Maryland, has already activated emergency teams and begun scheduling workers who might have to assess damage, restore power and coordinate with other power companies in the region, spokesman Marcus Beal said.

"We're already making plans and working as if this is a definite event," he said.

Officials in Pennsylvania, New Jersey and Massachusetts are monitoring the storm and getting prepared in case people need emergency supplies, volunteers or shelters.

In New Jersey, officials told people to be prepared for several days without electricity. Jersey Shore beach towns began issuing voluntary evacuations and protecting boardwalks. Atlantic City casinos made contingency plans to close, and officials advised residents of flood-prone areas to stay with family or be ready to leave. Airlines said to expect cancellations and waived change fees for passengers who want to reschedule.

New York City began precautions for an ominous but still uncertain forecast. No decision had been made on whether any of the city's public transportation outlets would be shut, despite predictions that a sudden shift of the storm's path could cause a surge of 3 to 6 feet in the subways.

"We want to make sure we are connecting with everybody and that we will have a game plan in place if the storm requires us to respond," said Paul Shipman, a spokesman for the American Red Cross in Connecticut and Rhode Island. He added that volunteers have already been called to be on alert.

The Red Cross will work with local media and local towns, and will use its social media outlets to get the word out about the storm, Shipman said. He encouraged iPhone and Android users to download the Red Cross' Hurricane app.

Sandy's landfall along the Mid-Atlantic coast "would likely be a billion-dollar disaster," according to Weather Underground meteorologist Jeff Masters. Additionally, Masters reminds the public that the full moon is on Monday, which means astronomical tides will be at their peak for the month, increasing potential storm surge flooding.

What's creating this monster? A combination of Hurricane Sandy and another storm over the eastern USA, writes meteorologist James Cisco of the Hydrometeorological Prediction Center in an online report.

The winds from Sandy, Cisco writes, will be "incorporated into a hybrid vortex over the Mid-Atlantic and Northeast next Tuesday." This "unusual merger ... should settle back toward the interior Northeast through Halloween, inviting perhaps a ghoulish nickname for the cyclone along the lines of 'Frankenstorm,' an allusion to Mary Shelley's gothic creature of synthesized elements."

Contributing: David Jackson, Yamiche Alcindor; Jeff Montgomery, The (Wilmington, Del.) News Journal; Florida Today; Associated Press.

USA TODAY