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 with life-threatening storm surges, forceful winds and rainfall that could cripple transportation and leave millions without power.
"Don't be stupid. Get out and go to higher, safer ground," New Jersey Gov. Chris Christie said today. "Let's get to work on this. We know how to do this. We've been through this before."
States of emergency were declared from North Carolina to Connecticut. Coastal communities in Delaware were ordered to evacuate by 8 p.m. tonight.
The storm 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.
"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."
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 "Perfect Storm," some meteorologists say.
The first rainfall from the megastorm is expected today and forecasters warn it could bring inland flooding around Maryland and Pennsylvania and up to two feet of snow in West Virginia.
Sandy remained at a Category 1 strength today, with 75 mph winds being measured. The storm was moving northeast at 10 mph, according to the National Hurricane Center.
FEMA administrator Craig Fugate urged people 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 are preparing for a shutdown of the subway system, the largest rapid transit system in the world, at 7 p.m. tonight. Sandy can 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.
"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," said Gov. Jack Markell of Delaware. "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."
Given its size and expected duration of two to three days, Hurricane 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 of 1950, FEMA administrator Craig Fugate said. But, Fugate said, officials don't try to make historical comparisons until after a storm hits.
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.
Gov. Chris Christie warned New Jersey residents they could be without power for a week to ten days. He said he is concerned residents may try to put generators indoors or run extenstion cords in a haphazard way to get electricity.
"That's a good general New Jersey rule: If it looks stupid, it is stupid," Christie said.
Sunday also brought hundreds of flight cancelations, with 3,700 expected for Monday, Flight Aware reported.
United Airlines, with a hub in Newark, N.J., has been the most aggressive so far in getting ahead of the storm. According to FlightAware, the airline has cancelled more than 300 flights today.
The airline told ABCNews the majority of those flights are scheduled for Sunday evening.
"United is working to operate a normal schedule to the east coast through the late afternoon hours. We have selectively canceled flights beginning this evening through tomorrow to many airports in the northeast and mid-Atlantic states," Rahsaan Johnson, an airline spokesperson, said in an email.
Many more cancelations from other carriers are expected.
People scheduled to fly to or from the eastern third of the country are encouraged to check their flight status.
ABC News' Sydney Lupkin and Genevieve Shaw Brown contributed to this report