Sandy threatens 11-foot wall of water, 2 feet of snow

Hurricane Sandy lumbered toward the densely populated East Coast early Monday, leaving millions of residents with only hours to prepare for its onslaught as forecasters warned that a wall of water up to 11 feet high could hit New York City. A day before the storm was scheduled to make landfall, state and local officials issued mandatory evacuation orders for hundreds of thousands of residents in low-lying areas and began the slow, grinding process of shutting down New York City's massive transit system. Authorities said the surge of seawater could swamp parts of lower Manhattan, flood subway tunnels and cripple the network of electrical and communications lines that are vital to the nation's financial center. Forecasters said Sandy has the ingredients to transform into a "super storm" as it merges with an Arctic jet stream, which could make the storm unlike anything seen over the eastern United States in decades. The storm is projected to make landfall late Monday . "We're looking at impact of greater than 50 to 60 million people," said Louis Uccellini, head of environmental prediction for the National Oceanic and Atmospheric Administration (NOAA). Sandy could be the largest storm ever to hit the United States, according to NOAA's website. 284,000 homes in danger? Worried residents in the hurricane's path packed stores, searching for generators, flashlights, batteries, food and other supplies in anticipation of power outages. Nearly 284,000 residential properties valued at $88 billion are at risk for damage, risk analysts at CoreLogic told Reuters. Grocery stores also reported runs on bread, bottled water and canned foods. The National Hurricane Center said early Monday that the storm has top sustained winds of 75 mph, with higher gusts. Hurricane-force winds were extending up to 175 miles from the storm's center. It was moving northward at 14 mph. It was expected to hook inland during the day Monday, colliding with a wintry storm moving in from the west and cold air streaming down from the Arctic. Forecasters said the combination could bring close to a foot of rain in places, a potentially lethal storm surge of 4 to 11 feet across much of the region, and punishing winds that could cause widespread power outages that last for days. The storm could also dump up to 2 feet of snow in Kentucky, North Carolina and West Virginia. Video: Record surges could produce 'worst-case scenario' (on this page) In a measurement of pure kinetic energy, NOAA's hurricane research division on Sunday ranked the surge and wave "destruction potential" for Sandy — just the hurricane, not the hybrid storm it will eventually become — at 5.8 on a 0-to-6 scale. The damage expected from winds will be far less, experts said. "The size of this alone, affecting a heavily populated area, is going to be history-making," said Jeff Masters, a hurricane specialist who writes a blog posted on the Weather Underground. 'Extraordinary situation' Weather.com predicted that "Sandy will be one of the strongest cyclones to hit the U.S. East Coast in years, with damaging winds, storm surge and rainfall flooding the primary threats." Stu Ostro, a senior meteorologist with The Weather Channel, warned that Sandy would  "occupy a place in the annals of weather history as one of the most extraordinary to have affected the United States." He added: "This is an extraordinary situation, and I am not prone to hyperbole." Hurricane Sandy was blamed for the deaths of 65 people in the Caribbean before it made its way north. Interactive: Hurricane Tracker (on this page) U.S. stock exchanges said they would not be trading on Monday and possibly Tuesday. In Washington, D.C., federal offices will remain closed Monday, and federal courts in affected areas announced they would be shuttered in anticipation of the historic storm. Workers on Sunday night began shutting down New York City's subway, bus and commuter railroads , as ordered by New York Gov. Andrew Cuomo. In New Jersey, bus, rail and light rail services were gradually shut down starting Sunday afternoon. BreakingNews.com's coverage of Sandy In anticipation of widespread damage and vast power outages, states of emergency were declared in North Carolina, Virginia, Maryland, Pennsylvania, New Jersey, New York, Connecticut, Rhode Island, Massachusetts and the District of Columbia. Story: States shutter transit systems ahead of storm "Sandy is a large hurricane and large systems pose multiple hazards for more people than … smaller systems of comparable intensity," National Hurricane Center Director Rick Knabb said Sunday. "The large size of the system is why it is so capable of producing a life-threatening storm surge, with that threat being applicable to many areas." Mandatory evacuations Forecasters said Sandy could make U.S. landfall anywhere between Maryland and southern New England. Some computer models show a likely landfall between Delaware and the New York/New Jersey area, where the storm surge — made worse by a because of giant waves and high tides due to a full moon — could reach from 6 feet to 11 feet. New York City Mayor Michael Bloomberg ordered mandatory evacuations (.PDF) of 375,000 people from low-lying areas in New York City, signifying officials' growing concern about the severity of the storm and its impact on the five boroughs. About 45,000 of those were people living in public housing, where the heat, hot water and elevator services will be turned off, Bloomberg said, according to NBCNewYork.com. Video: Bloomberg orders evacuation in NYC's low-lying areas (on this page) "This evacuation is mandatory. It is for your own safety," Bloomberg said. The city opened 65 shelters in public schools on Sunday morning and said more could be opened. Last year, the mayor called for an evacuation in anticipation of Tropical Storm Irene, which officials called unprecedented. Three other states also were ordering mandatory evacuations. Delaware Gov. Jack Markell ordered a mandatory evacuation of an estimated 50,000 people in coastal communities. In New Jersey, mandatory evacuations were ordered for Sandy Hook south to Cape May, an area that includes the casinos in Atlantic City and popular beach resorts. Five shelters were open in Atlantic County for those five affected municipalities that are home to some 66,000 people, according to census data, said Linda Gilmore, a county spokeswoman. One of the shelters was already full. "As conditions continue to deteriorate we're seeing more people," with rain and increasing winds, she told NBC News. Video: Hurricane Sandy: 400,000 told to evacuate (on this page) Connecticut Gov. Dannel P. Malloy ordered mandatory evacuations on Sunday in vulnerable areas of Bridgeport and Fairfield. Separately, several cities, including Stamford, Conn., and Islip, N.Y., also ordered residents out of flood-prone areas. Tips on preparing for Sandy Not everyone was heeding the evacuation orders. Peter Mercatanti, 26, who lives on Deauville Beach in Mantoloking, N.J., said Sunday afternoon that he had kayaks ready and had packed wet suits, waterproof book bags, flares, glow sticks, flashlights, propane and food to bear out the storm. He had stocked sandbags around his home and put up shelter blinds on all of the windows and the doors. But ocean water was hitting his fence and winds that he estimated to be about 25 to 30 miles per hour could be heard screaming on the beach. "I just wanted to be here for it, see it, experience it, and try to take care of my house as much as possible," Mercatanti, a chief of operations for a gym chain, told NBC News by telephone. Though he is "extremely worried," he won't leave the island but will head to a friend's house nearby if need be. "I've pretty much kind of prepared for every possible situation," he said. "I can be sustainable and floating." The Coast Guard also rescued a surfer near Sea Bright, N.J., where authorities have issued mandatory evacuations. "We can't stress enough to stay clear of beaches," said Chief Petty Officer Rodger Krass, the command duty officer in the New York sector, said in a statement. "Now is not the time to head out onto the water to go surfing as sea conditions are extremely dangerous and are continuing to worsen as Hurricane Sandy approaches shore." President Barack Obama on Sunday visited the National Response Coordination Center at FEMA Headquarters, where the deployment of federal resources and teams to states up and down the East Coast will be coordinated, the White House said. Calling it a "very serious storm event," he said: "This is going to affect a big swath of the country and because it's slow moving, it could be a number of days until people get power back." Video: Obama on storm: 'Take this very seriously' (on this page) FEMA Administrator Craig Fugate said earlier Sunday that the "time for preparing and talking is about over." "People need to be acting now particularly as this storm … is becoming a rather substantial risk to storm surge," he added. The hurricane is "going to produce very high potential life-threatening storm surge … that may require additional evacuations today." Coastal flooding posed a major threat, particularly in low-lying areas like New York City, the global financial nerve center, and Alexandria, Va., across the Potomac River from Washington, D.C. Flooding also could occur in parts of North Carolina, Virginia, Maryland, Connecticut, Rhode Island and New York, the National Hurricane Center said. But Fugate warned that "this is not a coastal threat alone" and that the impact will be felt "well inland." Share your images of Hurricane Sandy preparations Some areas could experience up to a foot of rain, while others, such as West Virginia, Virginia and the area around the North Carolina-Tennessee border, could get from 1 to 3 feet of snow. Sandy also was disrupting travel in the region. More than 6,800 flights have been canceled so far, according to FlightAware.com, a flight tracking website. Rail traffic also was impacted, with Amtrak canceling all of its northeast corridor service in addition to some other lines it operates in the region. Some local governments, including New York City and Washington, D.C., announced schools would be closed on Monday and Tuesday. Federal government offices in Washington, D.C., will also be closed Monday and non-emergency employees there as well as in Connecticut and Massachusetts have been told not to come to work. Election issues Coming in the hectic run-up to the U.S. presidential election on Nov. 6, the storm presented a challenge to the campaigns of Obama and his Republican challenger, Mitt Romney. Obama canceled campaign stops in Virginia and Colorado early next week because of the hurricane and was planning to remain at the White House, his spokesman said Saturday. Romney rescheduled his campaign events for Virginia on Sunday and headed to Ohio instead. Video: Hurricane Sandy could dampen Virginia campaigns (on this page) Obama said officials did not expect the storm to impact voting, "but we're obviously going to have a look." Meantime, Maryland's governor also announced that early voting in the state would be canceled Monday, so as not to jeopardize the safety of voters, NBC Washington reported. Sandy is set to deliver potential election surprise Power outages caused by the storm, expected to affect millions of residents and businesses, could continue through the election, NBC meteorologist Bill Karins warned. "After the storm hits, expect the cleanup and power outage restoration to continue right up through Election Day," Karins said. "Serious and life-threatening weather conditions are expected from Outer Banks to New England." Although Sandy is not forecast to be as strong as other recent storms to hit the Northeast — such as Hurricane Irene in August 2011, which left $4 billion in damage — it holds the potential to cause significant damage because it will be moving slowly. Some experts predict at least $1 billion in damage in the United States. Insurers prepare for impact of Hurricane Sandy Slideshow: Sandy sets sights on East Coast (on this page) NBC News staff, The Associated Press and Reuters contributed to this report.