"This is not a typical storm," Gov. Tom Corbett said Sunday. "It could very well be historic in scope and in nature and in magnitude because of the widespread anticipated power outages, flooding and potential major wind damage to the commonwealth."
Corbett and Philadelphia Mayor Michael Nutter declared states of emergencies. State office buildings in Philadelphia, city offices and Philadelphia schools were scheduled to be closed Monday. The Archdiocese of Philadelphia, the University of Pennsylvania and several other local universities canceled classes for Monday and Tuesday. And a class for new Philadelphia police recruits was delayed from Monday until later in the week.
The storm was expected to result from Hurricane Sandy coming ashore late Monday or early Tuesday, most likely in New Jersey, and colliding with a wintry storm moving in from the west and cold air streaming down from the Arctic. Forecasters warned that the resulting megastorm could wreak havoc over 800 miles from the East Coast to the Great Lakes.
Philadelphia's transit authority said it would shut down subways, commuter rail, buses and trolleys at about 12:30 a.m. Monday.
The American Red Cross opened evacuation centers in the area, and Philadelphia residents descended on supermarkets and local stores to buy supplies to ride out the storm.
At The Fresh Grocer in west Philadelphia, Tayna Lindsey, 38, was among those stocking up. She bought nearly $200 worth of food, including a turkey, and planned to cook as long as her power was on.
"If my kids are home," she said, "they need to eat. I have a big family."
She intended to prepare plenty of food for her husband, four children, a grandchild, other relatives and neighbors in case she needs to stay on the job at the Hospital of the University of Pennsylvania, where she works as a medical assistant.
Wade Green, 24, of Philadelphia left the store with a case of water and other supplies. But the new city sanitation employee said he has raingear ready and has been told that he might be working during the storm.
"I already know I'm going to be in the middle of it, so I'll be preparing for it," he said. "Prepare for the worst, hope for the best."
At a marina in Philadelphia's Penn's Landing section on the Delaware River, where about 20 people live on houseboats, people were helping one another secure lines but felt the floating dock and the condominiums on either side of the marina would help protect their vessels.
"We're going to be as safe here as we would be anywhere because we're going to be as high as the water gets, plus we've done the prep work," 62-year-old Howard Molt said.
Across the way, Hans Eriksson, 35, who lives on a houseboat with his wife and 19-month-old daughter, said they had spent 2 1/2 years sailing in the Caribbean so they feel they will be all right.
"If it starts looking dangerous, obviously we'll get off the boat," Eriksson said.
Peco Energy, the state's largest electric and gas utility, and PPL Corp., which has 1.4 million customers in 29 counties, said they each have hundreds of line and tree-trimming crews lined up if necessary.
Peco spokeswoman Karen Muldoon Geus said that she expects some customers to be without electricity for several days and that shutting down power to certain areas is likely in areas with heavy flooding. The utility will also have trailers with response crews in flood-prone areas to quickly turn off gas service where necessary.
In parts of western Pennsylvania, the National Weather Service issued a flash flood watch for areas that could get more than 2 inches of rain Monday and Tuesday. Winds were expected to reach 25 to 35 mph with gusts of 50 to 60 mph, and snow was expected later in the week.
Emergency management officials said that although flooding might not be as bad as in recent storms, they were very concerned about winds that could cause significant damage and sustained power outages.
"This has the potential to really be a historic storm in terms of impact here in Pennsylvania," Pennsylvania Emergency Management Agency spokeswoman Ruth Miller said. "We expect a lot of trees and power lines to be down."
State transportation crews were ready to clear roadways, while state conservation officials had state firefighting teams equipped with chain saws and debris-clearing equipment, she said.
The Pennsylvania National Guard has told about 16,000 members to be ready to deploy for a storm response if needed. On Monday, 750 guardsmen will be activated in southeastern Pennsylvania and 775 more will be activated in other areas of the state, while guard helicopters would be activated Tuesday for possible for rescues, spokesman Maj. Edward Shank said.
Halloween parades in Allentown, Bethlehem and other communities have been canceled or postponed.
In Franklin County in central Pennsylvania, the 70th annual Mercersburg Halloween parade planned for Monday was canceled for just the second time in 70 years, the Herald-Mail of Hagerstown, Md., reported.
On South Street in Philadelphia, Colin Taylor was waiting at a bus stop when he learned the transit system would be shut down Monday. He said he hadn't heard much about the storm because he doesn't have a TV and his computer is broken. So he didn't have much food at home to celebrate his 22nd birthday Monday.
"I was in Vermont for (the remnants of Hurricane) Irene," said Taylor, who graduated from Bennington College in Vermont. "When you went out and saw the destruction, that was really scary. But I'm assuming the city of Philadelphia is better prepared than Vermont."
Associated Press writer Ron Todt in Philadelphia contributed to this report.