Sandy regained hurricane strength Saturday, as weather forecasts predict it will turn into a destructive "superstorm" that will impact the Eastern Seaboard as early as Sunday.
This storm will be studied for years to come, said Louis Uccellini, who is responsible for environmental prediction at the National Oceanic and Atmospheric Administration.
CNN Weather estimates damage from Hurricane Sandy could reach $3.2 billion. This estimate is based only on wind damage and does not include flooding.
At least four states in its path, as well as the nation's capital, have declared states of emergency, and some airlines have announced they will allow passengers to change existing flights to and from Atlantic coast cities free of charge.
How is Sandy expected to develop?
Weather forecasters still predict it will push in a large storm surge as it nears land, inundate a broad, highly populated region with rain, and knock out power for perhaps weeks with its broad, destructive winds.
"Forget about the category with this," said CNN meteorologist Rob Marciano. "When you have trees with leaves on them still, this kind of wind and rain on top of that, you're talking about trees that are going to come down, power lines are going to be out and the coastal flooding situation is going to be huge."
Sandy is still predicted to merge with a strong cold front from the west and morph into a "superstorm."
This "will energize this system, so we'll actually get an intensification of this system," Uccellini said.
The resulting storm could sit over New England, making untold trouble for millions of residents, even dumping heavy snow in the Appalachians.
"Expect it to move very slowly," said James Franklin of the National Hurricane Center. "The large size of the system and its slow motion will mean a long-lasting event with two to three days of impacts."
The tropical storm force winds will likely spread over a vast distance, potentially up to 700 miles across, stretching from North Carolina to Maine, which could mean widespread power outages, according to CNN's Weather Unit.
Sandy has taken on a lopsided form, and its heaviest winds should be in the northern and eastern sections of the storm as it nears land -- and be directed inbound toward the coastline.
The surge is likely to hit during a full moon, when the tides are the highest, exacerbating coastal damage.
Computer models predict Delaware, Maryland and Virginia could see up to a foot of rainfall, according to the CNN Weather Unit. Isolated spots could see the worst rains in 500 years.
At 8 a.m. ET Saturday, the National Weather Service said Sandy was about 335 miles south-southeast of Charleston, South Carolina. It was a Category 1 hurricane with winds of 75 mph.
The U.S. target area is hard to predict at this point. Some landfall computer models show the storm striking somewhere between the border separating North Carolina and Virginia north to Connecticut, some of the most densely populated areas of the country.
Sandy's death toll for the week rose to 22 Saturday. Police in Puerto Rico reported the death of a man who drowned attempting to cross a river Friday that had flooded due to rains then Hurricane Sandy dumped when it passed over.
How will Sandy effect voting and election campaigning?
With a national election already under way in many early-voting states, Sandy's wrath could have a ripple effect on politics.
In Virginia Beach, a campaign rally scheduled for Sunday for GOP presidential hopeful Mitt Romney was canceled because of Sandy. There was no word yet on the status of other events scheduled later in the week. "We're keeping an eye on it," said a senior campaign adviser.
Similarly, Vice President Joe Biden canceled his visit to Virginia Beach on Saturday, "out of an abundance of caution to ensure that all local law enforcement and emergency management resources can stay focused on ensuring the safety of people who might be impacted by the storm," the Obama said.
Bad weather in Maryland or the nation's capital could make it harder for people to get out and cast their ballots. Early voting kicked off Monday in Washington and is scheduled to start Saturday in Maryland. On Friday, Maryland Gov. Martin O'Malley warned that his state's early voting could be affected by the pending storm, leaving open the possibility that the vote could be rescheduled, or polling stations relocated inland.
What preparations are being made?
The District of Columbia, Pennsylvania, Maryland, Virginia and New York have declared states of emergency, while Maine's governor signed a limited emergency declaration. Delaware's governor has said the state will issue a mandatory evacuation of its coastline, if the storm stays on path.
North Carolina issued states of emergency for 40 coastal counties.
All the Northeast metro airports will see flights delayed and canceled, the CNN Weather Unit said.
American, United and Spirit announced late Friday they will waive changes fees for passengers traveling in and out of many Atlantic coast cities.
Amtrak will deploy preparedness crews and equipment along its tracks in the Northeast to remove debris, make repairs and mend any downed electrical lines, it said in a statement Friday.
Washington, D.C.'s power company has ordered 2,500 additional linemen, 400 tree cutters and has staffed beefed up call center staff, according to affiliate WJLA. "We'll open up additional staging areas," PEPCO executive David Velazquez said.
In New York, the Metropolitan Transportation Authority is studying whether it should suspend all or some services ahead of the storm, according to Mayor Michael Bloomberg.
In Maryland, the Baltimore Gas and Electric Company expects that several hundred thousand customers could be affected, as early as Sunday.
Late Friday, shoppers depleted pallets of mineral water stacked up outside a supermarket in Staten Island, New York. At 11 p.m. the parking lot was still full of people buying storm supplies, affiliate WABC reported.
In New York City, workers covered subway ventilation grids to keep potential flood water out. Bulldozers shored up sand to form barriers in hopes of preventing street flooding in coastal areas of the city's Burroughs.
They did the same on New Jersey's shores as early as Thursday, CNN KYW reported. Worried residents filled sandbags in case of flooding.
"We will be piling up as much sand as possible along the beachfront," said Frank Ricciotti, Margate, New Jersey, public works director. "I think the water damage is worse than another type of damage, and the hardest thing is to stop water, once it starts coming up."
Residents in New Jersey have been stocking up on batteries and bottled water since Thursday, and hardware stores have put up preparedness displays, CNN affiliate KYW reported. One location quickly sold out of electric generators.
"This is the worst timing for a storm," Newark Mayor Cory Booker told CNN's Soledad O'Brien. "You have fall ending, a lot of loose branches.
"The storm itself will be bad, but I worry about the aftermath, people being caught without power."
Farther south, in the Norfolk, Virginia, area, more than two dozen ships were being sent to sea for their own protection. Sailors at the naval base stacked up sand bags in preparation.
Is Sandy another "Perfect Storm?"
Sandy presents a scenario not unlike the one that led to 1991's "Perfect Storm," when moisture flung north by Hurricane Grace combined with a high pressure system and a cold front to produce a tempest in the north Atlantic over Halloween.
But Grace never made landfall.
Multiple calculations of its path predict with that Sandy will.