NEW YORK — East Coast residents prepared Saturday for the onslaught of Hurricane Sandy, which forecasters expect to make landfall as soon as Monday night and then merge with a sprawling winter storm to create weather havoc for tens of millions of people across one-third of the nation.
From Maine to the Carolinas, federal and state officials urged residents and businesses to prepare for the worst — drenching rain, flooding, high winds, highs seas, snow and widespread power outages. Federal officials said the impact would extend into the Ohio Valley.
Even though Sandy was still at least two days away, residents along the northeastern Atlantic Coast, mindful of possible transit shutdowns and bombarded by storm warnings, kicked into preparation mode.
PHOTOS: Hurricane Sandy
Battery-operated lanterns, batteries, flashlights, tape, plastic tarps and rope vanished from shelves at hardware stores like Brown's, on the Rockaway peninsula in the New York City borough of Queens.
But nothing was in as much demand as sandbags, said Brown's owner Noni Signoretti, as customers lined up at cash registers. "We got 1,000 in, and within an hour they were gone," she said. The shop was expecting to receive 4,400 additional sandbags, and it planned to open two hours earlier than normal Sunday to accommodate the expected rush.
Like some on the peninsula, which was under a mandatory evacuation order when Hurricane Irene hit last year, Signoretti blamed much of the rush for supplies on the media frenzy surrounding Sandy.
"It's very similar to what we had with Irene — the panic," she said. "And what's happening today is that the weather is so nice that people have the opportunity to walk around in a panic."
Indeed, the wind was relatively calm, the ocean waves were no bigger than normal, and the boardwalk was dotted with its usual Saturday array of joggers, dog walkers and residents sitting on benches staring out at the water.
Neither Signoretti nor one of her regular customers, Jeanette Bernstein, planned to leave if an evacuation order was issued. Bernstein heeded last year's order after preparing her home for flooding that never came.
"I saved the sandbags from the last time," said Bernstein, who planned to flood-proof her home this year with sandbags, plastic and boards hammered over the windows. But she said her days of fleeing storms were over.
"I've been here so many years, I remember the flood when we were in rowboats," Bernstein said. That was Hurricane Donna of 1960, which sent the ocean and the bay washing over the peninsula. "If I lived through that," she added, "I can live through anything."
In New Jersey, Gov. Chris Christie warned against such complacency even as he sympathized with skepticism about forecasters' predictions. "We have to be prepared for the worst here," he said. "I can be as cynical as any of you, but when the storm comes, if it's as bad as they're predicting it will be, you're going to wish you weren't as cynical."
Dozens were killed as Sandy passed through the Caribbean late last week. The storm weakened but was upgraded Saturday to a Category 1 hurricane and was expected to turn west and make landfall late Monday or early Tuesday, with forecasters suggesting Delaware or southern New Jersey as possible locations.
The storm is expected to merge with a cold front from Canada — creating a dangerous system that could reach 800 miles in diameter, affecting a third of the United States. Winds up to 75 mph were measured Saturday as far as 100 miles from the eye of the storm, which remained over the ocean.
Even before Sandy makes landfall, conditions are going to get worse, said Rick Knabb, director of the National Hurricane Center.
"There's no avoiding a significant storm surge event over a large area," Knabb told reporters. "We just can't pinpoint who's going to get the worst."
Flood warnings are in effect in four states. Storm surges up to 4 feet were expected in parts of Delaware, and more than 2 feet of snow could bury West Virginia. A vast area from Virginia to New York could see up to 8 inches of rain over the next week.
"Don't get lulled tomorrow when there's not a lot of rain and not a lot of wind," New York Mayor Michael R. Bloomberg said at a news conference Saturday. "This is a dangerous storm. I think we're going to be OK, but if it were to strengthen unexpectedly or change its expected path, it could do a lot of damage."
The storm may cause major disruptions for travelers going to and from the East Coast over the next several days. Airlines said they were closely monitoring the storm, and they urged travelers to regularly check the status of their flights.
Several major airlines waived fees for passengers wanting to change their reservations, subject to some restrictions. Delta Air Lines said travelers could change flights at no cost for travel to 15 states and Washington, D.C. United Airlines made a similar offer to reschedule flights for no fee for travel in and out of nearly 30 airports along the East Coast.
Hurricane Sandy had already forced President Obama's campaign to scuttle one of Vice President Joe Biden's two scheduled stops in Virginia on Saturday. Aides to Republican presidential nominee Mitt Romney say they are canceling their travel to make sure they don't get in the way of state and local officials bracing for the storm.
Susman reported from New York and Serna from Los Angeles. Christi Parsons and Michael A. Memoli in the Washington bureau contributed to this report.