Hurricane Sandy _ upgraded again Saturday just hours after forecasters said it had weakened to a tropical storm _ headed north from the Caribbean and was expected to pummel the eastern United States.
The U.S. National Weather Service said the storm is likely to make landfall early Tuesday near the Delaware coast, then hit two winter weather systems as it moves inland. That may create a rare hybrid monster storm that could bring nearly a foot (30 centimeters) of rain, high winds and up to 2 feet (60 centimeters) of snow.
Experts said the storm could be wider and stronger than Irene, which caused more than $15 billion in damage when it struck in August 2011, and could rival the worst East Coast storm on record.
On Saturday morning, forecasters said hurricane-force winds of 75 mph (120 kph) could be felt 100 miles (160 miles) away from Sandy's center.
Sandy killed more than 40 people in the Caribbean, wrecked homes and knocked down trees and power lines. Early Saturday, the storm was about 155 miles (250 kilometers) north of Great Abaco Island in the Bahamas and 350 miles (565 kilometers) south-southeast of Charleston, 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.
Up and down the east coast of the United States, people were cautioned to be prepared for days without electricity.
"Be forewarned," Connecticut Gov. Dannel P. Malloy. "Assume that you will be in the midst of flooding conditions, the likes of which you may not have seen at any of the major storms that have occurred over the last 30 years."
On the shore of New Jersey state, 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. Several governors declared states of emergency. Airlines said to expect cancellations and waived change fees for passengers who want to reschedule.
"It's looking like a very serious storm that could be historic," said Jeff Masters, meteorology director of the forecasting service Weather Underground.
With a rare mix of three big merging weather systems over a densely populated region, experts predict at least $1 billion in damage.
Sandy, having blown through Haiti and Cuba and leaving 43 dead across the Caribbean, continued to barrel north. A wintry storm was moving across the U.S. from the west, and frigid air was streaming south from Canada.
If they meet Tuesday morning around New York or New Jersey, as forecasters predict, they could create a big, wet mess that settles over the nation's most heavily populated corridor and reaches as far west as Ohio.
Government forecasters said there is a 90 percent chance _ up from 60 percent two days earlier _ that the East Coast will get pounded.
"It's going to be a long-lasting event, two to three days of impact for a lot of people," said James Franklin, forecast chief for the National Hurricane Center.
At a Home Depot in Freeport, on New York's Long Island, Bob Notheis bought sawhorses to put his furniture on inside his home.
"I'm just worried about how bad it's going to be with the tidal surge," he said. "Irene was kind of rough on me and I'm just trying to prepare."
After Irene left millions without power, utilities were taking no chances and were lining up extra crews and tree-trimmers. Wind threatened to topple power lines, and trees that still have leaves could be weighed down by snow and fall over if the weight becomes too much.
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 (90 to 180 centimeters) in the subways.
The subway system was completely shuttered during Irene, the first such shutdown ever for weather-related reasons. Irene largely missed the city, but struck other areas hard.
The storm loomed a little more than a week before Election Day, while several states were heavily involved in campaigning, canvassing and get-out-the-vote efforts. Republican presidential nominee Mitt Romney and Vice President Joe Biden both canceled weekend campaign events in coastal Virginia Beach, Virginia, though their events in other parts of the states were going on as planned.
Some have compared Sandy to the so-called Perfect Storm that struck off the coast of New England in 1991, but that one hit a less populated area.
"The Perfect Storm only did $200 million of damage and I'm thinking a billion" this time, Masters said. "Yeah, it will be worse."
The worst East Coast storm on record was a 1938 New England hurricane that is sometimes known as the Long Island Express, which killed nearly 800 people.