The list of closures, delays, and suspensions grew throughout Friday as Irene meandered up the coast.
For the first time in its history, SEPTA is planning to suspend all service in Philadelphia and the suburbs, from 12:30 a.m. to noon Sunday.
The Delaware River Port Authority warned that bridges to New Jersey could be closed and PATCO shut down, and most flights at the airport are sure to be grounded.
Mayor Nutter is urging people to stay off the streets and hunker down through the storm, the worst of which should arrive about midnight and punish the region until about 3 p.m. Sunday.
"That is a lot of time for an intense combination of heavy rain and high winds," Nutter said.
While New Jersey looks poised to take the brunt of Irene's fury, Philadelphia and the Pennsylvania suburbs were predicted to see six to nine inches of rain and winds gusting up to 70 m.p.h.
In Darby Borough, officials ordered an evacuation for low-lying areas surrounding Darby Creek. All residents were advised to clear out by 8 p.m. Saturday. The Darby Recreation Center would be open as a shelter staffed by the Red Cross, police said.
Mandatory evacuations were not ordered in Philadelphia, but Nutter warned residents living in flood-prone areas to make plans to stay with friends or relatives.
"All Philadelphians . . . need to use common sense," he said. "Don't wait until you have water in your house to try to figure out what to do."
The city plans to open three high schools - Roxborough, Bartram and Lincoln - as shelters at 6 p.m. Saturday. Those three were chosen for their proximity to the city's creeks and rivers most susceptible to flooding.
City parks and recreation centers will close at 6 p.m. Saturday, and the city plans to open its Emergency Operations Center on Spring Garden Street at the same time. From there, officials will monitor Irene and plan any necessary response.
"This is one of those situations that's pretty much all hands on deck," Nutter said. "This is almost like a massive snow event in the winter."
SEPTA spokesman Richard Maloney said officials met Friday morning to discuss the storm and assess the wisdom of keeping the various transportation systems running.
"We finally came to the conclusion that none of us expected at the beginning of the meeting," he said. "We do not want people stranded. . . . We could have people in buses swept away in a storm that no one could get out to rescue them."
Several Regional Rail lines that get power from Amtrak are scheduled to be shut down at 5 p.m. Saturday: the Chestnut Hill West, Paoli, Airport, Trenton, and Wilmington lines.
The DRPA said officials there would monitor the storm's effects on the bridges and PATCO. The RiverLink ferry and Ben Franklin pedestrian walkway will be closed Saturday and Sunday.
The city is stepping up its efforts to get homeless people off the streets, and public buildings and shelters will have an "open door" policy, said Sister Mary Scullion, cofounder of Project HOME.
The Philadelphia Fire Department will have additional medics and rescue vehicles on hand, said Chief Richard Davison.
"That's a given," he said. "It's the first thing on the list."
Three area universities - Temple, St. Joseph's and Holy Family - rescheduled move-in and orientations set for this weekend.
Cultural institutions and tourist attractions such as the Philadelphia Museum of Art and Independence National Historical Park will be closed Sunday, and the Phillies canceled the second game of Saturday's doubleheader.
The hurricane has even disrupted the Jewish tradition of burying the dead as soon as possible. Cemeteries in Pennsylvania and New Jersey have told funeral homes they will be closed Sunday.
One business that seemed determined not to be interrupted was Pennsylvania's casinos. With a mandatory evacuation shutting down Atlantic City, all three Philadelphia area casinos - Parx, Harrah's Chester, and SugarHouse - said they planned to stay open during the storm.
Government advisories issued Friday were unanimous in urging people to take precautions - have nonperishable food and water, battery-powered radio and flashlights, and medication on hand.
"We need everyone to take this matter very seriously," Nutter said. "All of us need to be prepared."
Contact staff writer Troy Graham at 215-854-2730, firstname.lastname@example.org or @troyjgraham on Twitter.
Contributing to this article were Inquirer staff writers Jennifer Lin, Jeff Gammage, Sally A. Downey, and Mari A. Schaefer.