Residents up and down the East Coast are preparing for what forecasters predict could be the worst storm in two generations as Hurricane Sandy is strengthening, putting 50 million people at risk.
The eye of Sandy is forecast to make landfall late Monday night in Atlantic City, N.J., bringing with it life-threatening storm surges, forceful winds and rainfall that could cripple transportation and leave millions without power. But the force of the storm was already evident as powerful winds and high seas already began lashing the coast Sunday night.
The size and power of the storm are almost without equal as several systems will combine to wreak havok on a large section of the nation -- from North Carolina to New England as far west as the Great Lakes.
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Hurricane Sandy's maximum sustained winds increased to 85 mph overnight. As of 5 a.m., Sandy was centered about 385 miles southeast of New York City, and moving north at 15 mph, according to the National Hurricane Center.
On the East Coast, a storm surge is expected along a 600-mile stretch of the Atlantic along with rainfall in places of 6 to 10 inches and even more, and waves 20 to 25 feet are possible on the south side of Lake Michigan Monday night into Wednesday.
"We want to prepare people for the worst," New Jersey Gov. Chris Christie said Sunday, warning that some residents could be without power for more than a week.
As of 6 a.m. today, Jersey Central Power and Light was reporting 4,671 customers without power in northern New Jersey, according to ABC News' New York station WABC-TV.
Christie urged people in the path of Hurricane Sandy to "remain calm and listen to instructions."
A wind gust of 64 mph was recorded just south of Wilmington, N.C., shortly before 5 a.m. today. The highest rainfall total recorded was almost six inches in Dare County, N.C.
Tens of thousands of people in coastal areas have been ordered to evacuate their homes before Hurricane Sandy pounds the eastern third of the United States.
States of emergency were declared from North Carolina to Connecticut. Coastal communities in Delaware were ordered to evacuate by 8 p.m. Sunday night, and all non-emergency vehicles were ordered to stay off the state's roads beginning at 5 a.m. Monday.
"While the predicted track of Hurricane Sandy has shifted a number of times over the last 24 hours, it has become clear that the state will be affected by high winds, heavy rainfall, and flooding, especially along the coastline for a several day period," Delaware Gov. Jack Markell said. "These factors, along with the potential for power outages, have convinced me that the prudent thing to do is have people leave most of our coastal communities."
Sandy is expected to bring potentially life-threatening storm surges on the coast, ranging from several feet to potentially as high as 11 feet in the Long Island Sound area of New York, said Rick Knabb, director of the National Hurricane Center.
Sandy will meet up with cold front coming from the northwest and a high pressure system from Greenland, fueling it with enough energy to make it more powerful than the so-called "Perfect Storm" in 1991, meteorologists say.
"The size of the storm is going to carve a pretty large swath of bad weather," Knabb said. "This is not just a coastal event."
The first rainfall from the megastorm already began to hit the coast of Virginia, Delaware and New Jersey Sunday night and forecasters warn it could bring inland flooding around Maryland and Pennsylvania. A blizzard warning was issued for portions of West Virginia, where Sandy could bring up to two feet of snow.
FEMA administrator Craig Fugate urged people in Sandy's path to take the storm seriously and to heed any evacuation orders.
"The time for preparing and talking is about over. People need to be acting now," Fugate said.
New York City transit officials shut down the subway system, the largest rapid transit system in the world at 7 p.m. Sunday. Sandy could potentially create a storm surge capable of overtopping the Manhattan flood walls, filling the subway tunnels with water.
New York City Mayor Michael Bloomberg ordered the evacuation of areas of lower Manhattan and the Rockaways.
"If you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you," Bloomberg said at a news conference. "This is a serious and dangerous storm."
New York City Schools will also be closed Monday, Bloomberg said.
Given its size and expected duration of two to three days, Sandy could turn out to be comparable to 1991's Hurricane Grace, also known as the "Perfect Storm," and a cyclone that struck near the Appalachians in November 1950, FEMA administrator Craig Fugate said. But, Fugate said, officials don't try to make historical comparisons until after a storm hits.
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Power companies are being proactive before Sandy makes landfall, trimming trees and putting equipment place to hopefully minimize the number of people left without power after the storm.
Last year, Hurricane Irene left 7 million homes without power in the same area Sandy is expected to batter with wind and rain.
"The best thing is to be prepared, and I think that's where we are. We're prepared for what the worst will bring," said Vince Maione, who has been with Atlantic City Electric, a company serving south New Jersey, for 28 years.
As of this morning, 6,500 flights in the U.S. had been cancelled, according to Flight Aware.
People scheduled to fly to or from the eastern third of the country are encouraged to check their flight status.
ABC News' Russell Goldman, Sydney Lupkin and Genevieve Shaw Brown contributed to this report