"Philadelphia is in the path," Mayor Nutter warned about 10:30 p.m. "We will see very severe winds, four to eight inches of rain in a very short period of time. . . . We will get through this, because we are prepared."
Caravans of power-company trucks from Southern states were barreling toward the Northeast on I-95 to be in position to assist with anticipated power outages from 70 m.p.h. wind gusts.
The storm could wobble or weaken, but both the National Hurricane Center and Accuweather predicted it would make landfall just north or just south of Atlantic City, which like some other towns already was starting to flood Sunday from high surf.
Officials across the region - from the Shore to Philadelphia, to the heart of Pennsylvania - warned of a huge, destructive weather mass with drenching rains and high sustained winds that could bring down power lines and topple trees. The threat of flooding stretched west to Harrisburg. Rain could turn to snow in the mountains of Western Pennsylvania. Storm surges on ocean beaches could be six to 10 feet.
Most of the Philadelphia region's economy will grind to a halt. Taxi services, malls, universities, and government agencies have announced one- or two-day closures. At the airport, all flights are canceled for Monday.
On Sunday, people waited in lines for gasoline, and supermarkets ran short of peanut butter, bread, and water.
A major threat was storm surges that could erode beaches and damage property.
"This is a storm surge you'll see once in 50 years. That's the kind of thing that's coming," said Jack Boston, expert senior meteorologist with Accuweather.
Philadelphia can expect gusts of near-hurricane force Monday night and rain of four to eight inches between Monday and Wednesday. Boston called Hurricane Sandy a "hybrid between a nor'easter and a hurricane" because of its size.
Gov. Corbett declared a state of emergency and said at a news conference that 1,600 National Guard troops were prepared to help in the event of a disaster. "We are prepared for the worst and hope for the best," he said.
Gov. Christie said all schools in Gloucester, Salem, and Mercer Counties would be closed Monday and Tuesday. He ordered closure of state offices and suspension of NJ Transit services.
Late Sunday night, Delaware Gov. Jack Markell declared that only essential personnel - those necessary for public safety, government functions, health services and food deliveries - were allowed on the state's roadways beginning early Monday morning.
"People have had several days to be out preparing for the storm's arrival. When Sandy hits on Monday, they should be at home or if necessary a shelter to wait out the worst of the storm," Markell said. ""Do not put yourself on the road. Do not put yourself - and those who may need to rescue you - at risk."
School, transit, and city officials in the Philadelphia area were taking nothing for granted as Sandy bore down.
Mayor Nutter said he spoke with President Obama on Sunday about the storm and the mayor pleaded with Philadelphia residents in river-prone neighborhoods to seek safety in city-run shelters or with family members. He announced that city government would be closed Monday. "The intensity is not lessening," the mayor said. "It's actually strengthening. Every concern that we've laid out for the past couple of days is in fact real."
Nutter said extra police and fire personnel would be on duty through the storm and that roads needed to be clear for them. "If you don't need to be out tomorrow, please stay home," he said Sunday.
City trash will not be picked up Monday. City residents with Monday pickup days were asked to keep their trash for an extra week.
The city opened three shelters at 4 p.m. Sunday, and residents seemed to be heeding the mayor's alarm.
Between 4 and 5 p.m., about two dozen people streamed into West Philadelphia High, dragging small suitcases and carrying bags.
Cots with blankets filled the shelter area, and bottled water and food arrived soon after the shelter opened. Members of the media were not allowed into the shelter, with the city's Office of Emergency Management and Red Cross personnel citing concerns about adding to the individual trauma.
The School District of Philadelphia said it would close schools Monday, and Catholic schools will be closed Monday and Tuesday. Dozens of suburban districts in Pennsylvania and South Jersey also canceled sessions.
Alex Klein, a junior at University of Pennsylvania majoring in urban studies, said he and his five roommates ran to the grocery store to stock up for the storm when they heard the university had canceled classes Monday and Tuesday. They already had jugs of water on hand from a delivery service. They had stocked up on flashlights, batteries, food, and candles.
"Everyone has exams coming up, and Thanksgiving isn't far away," Klein said. "If worse comes to worst, we'll just study. We've got candles."
While government officials were quick to respond to the threat, so were businesses and retail stores Sunday.
All the region's major malls, including King of Prussia, said they would not open Monday.
In Center City, building owners planned to put up maintenance staff in hotels overnight so that high-rise towers could be open Monday morning.
PATCO said Sunday night that bridges - Walt Whitman, Betsy Ross, Commodore Barry, and Ben Franklin - would remain open unless winds grew dangerously high. Officials will monitor weather reports closely, he said.
Many municipalities issued their own storm warnings.
In Bucks County, Lower Makefield Township declared a state of emergency beginning at 6 a.m. Monday and said that nonessential cars and trucks are prohibited on the town's roads and nonessential businesses are to close.
In nearby Yardley, just yards from the Delaware River, Eben Copple, executive chef at the Yardley Inn, vowed: "We are going to continue as if things are normal. We are not expecting deliveries [on Monday], so we'll rewrite our menu to accommodate for the storm. But that's OK, we'll make do."
In Royersford, Montgomery County, residents along the Schuylkill were asked to voluntarily evacuate before Sandy hits, County Commissioner Josh Shapiro said at a news conference.
Residents in other county areas, including Pottstown, Mont Clare, Norristown, Conshohocken, Glenside, and Whitemarsh were being urged to consider evacuating.
Despite the storm anticipation, Sunday seemed just another fall day for some. The Eagles played - and lost - at the Linc. A regatta went ahead on the Schuylkill.
Ellen Carver, codirector of the Head of the Schuylkill Regatta, said only one race was stopped because of the wind.
"Other than that it was a wonderful day of racing," Carver said.
Elsewhere, residents were stocking up on bread and nonperishables and filling up gas tanks.
At Wegmans in Cherry Hill, crowds were steady all day, said merchandising manager Amanda Mancini. Despite the rough weather ahead, the store planned to keep regular hours - 6 a.m. until midnight.
"We have ice. As of this moment we have water. I can't guarantee we're going to have water in the next 10 minutes," Mancini said just after dark.
The store was out of batteries and flashlights but had plenty of groceries - she wasn't worried they were going to run out, Mancini said. But there was definitely a run on certain items. "We've sold a lot of potato chips, a lot of cookies. Lots of peanut butter and jelly," Mancini said.
At the Whole Foods on South Street, a cashier said they had run out of gallon-size bottles of water. "We still have a good bit of one-liters and the smaller bottles," he said. The store was also sold out of eggs.
Karen Muldoon Geus, a Peco spokeswoman, said the utility had 300 line crews and 150 tree crews on standby.
Utilities from Chicago, Tennessee, Kentucky, Mississippi, and Louisiana were dispatching crews to assist.
Peco had positioned trailers near flood-prone areas to act as operations centers during power restoration activities, she said.
"We expect if we get a direct hit, the storm will result in a multiday restoration effort," Geus said.
In Camden County, authorities announced they had ordered all county parks closed at 2 p.m.
Streets emptied in Sea Isle City and Ocean City as flooding began at 11 a.m., with some main roads in Sea Isle completely impassable. Traffic clogged the Garden State Parkway early Sunday, with tolls waived for residents on their way to the mainland.
As weather services focused on Atlantic City as Hurricane Sandy's landfall, the casino town quickly emptied out on Sunday, with hundreds of residents and vacationers lining up at the city's convention center to board buses for emergency shelters.
Casinos closed shop as early as noon. Some vacationers said they had planned to wait out the storm at the blackjack tables and the Trump Plaza but were turned away.
Waiting to board a bus outside the convention center, Tamika Brooks, of Atlantic City, stood behind a long line of residents trying to get out of the city. She said she had no idea where the bus was taking her, but wanted to heed Christie's mandatory evacuation order.
"I'm not worried," she said, laughing. "Right now I just want to go to sleep - I've been up since 5 a.m. getting ready."
Contact Bob Fernandez at 215-854-5897 or email@example.com.
Inquirer staff writers Kristen A. Graham, Jonathan Lai, Jessica Parks, Linda Loyd, Amy S. Rosenberg, Diane Mastrull, Aubrey Whalen, Maria Panaritis, and Andrew Maykuth contributed to this article.