Like the Perkiomen, which rose nearly three feet above flood stage, other streams in the region reached higher-than-expected crests on Wednesday.
Police blocked off washed-out roads in Whitemarsh, where only a week earlier National Guard troops had evacuated residents along the brimming Wissahickon Creek.
The Schuylkill lapped over its banks in Philadelphia, adding to morning commuting woes.
City police announced Wednesday night that flooded Kelly Drive would remain closed through Friday morning.
Lt. Raymond Evers, a police spokesman, said the National Weather Service predicts the Schuylkill will recede to 10.5 feet early Thursday morning before rising to 12.8 feet Friday.
"This is of course based on the river forecasts, which have been less than reliable for this event," Evers said.
The city's Office of Emergency Management will issue another forecast for the river Thursday morning, Evers said.
The Delaware spilled onto River Road in Upper Makefield, Bucks County, and was forecast to exceed flood stage Thursday morning at Trenton.
A downed tree near the Berwyn train station in Chester County knocked out service on SEPTA's Paoli line, and Amtrak suspended service from Philadelphia to Harrisburg, where heavy rains from stalled thunderstorms led to evacuations and a state of emergency. The Susquehanna is forecast to crest seven feet above flood stage Friday morning.
About three inches of rain fell in Philadelphia Tuesday and Wednesday. So far this year, the region has had about 13 months' worth of precipitation - close to 45 inches.
A half-foot or more has fallen just this week in parts of central Pennsylvania. Downpours have caused flooding and some evacuations in the Harrisburg area and in parts of northeastern Pennsylvania.
Gov. Corbett held a news briefing Wednesday night to say that record flooding was occurring on some creeks and that the Susquehanna River was set to crest late Friday at near-record levels with the potential for wide-ranging damage and evacuations - possibly even including the governor's mansion.
In the Philadelphia area, more showers were anticipated Thursday, with the chance of even more through the weekend.
Meanwhile, yet another tropical storm is taking shape in the Gulf of Mexico.
"The pattern has not changed," said Henry Margusity, a meteorologist with AccuWeather Inc. "It's really crushing us."
Salamone, 45, a building contractor, will second that. Irene sent three feet of water into his kitchen, bathroom, and living room, causing $10,000 in damage. He doesn't know when he'll have the time or money to repair it. The rotten weather has hurt his business.
His house escaped major flood damage Wednesday, but the threat of further downpours was a source of major anxiety.
Why has the region turned into a rain forest?
Oddly, it may be related to the incredible drought conditions in Texas, said Ed O'Lenic, operations branch chief at the government's Climate Prediction Center outside Washington.
That drought is part of a larger air-circulation pattern that has helped shunt moisture to the East. A busy tropical-storm season also has played a role in supplying copious rainfall.
"The Gulf of Mexico is quite warm, and almost anything that gets in there develops into a tropical storm," he said.
The upshot has been a historically rainy late summer.
"It makes you wonder what's going to happen later in September," said Jim Poirier, a meteorologist with the National Weather Service in Mount Holly.
Contact staff writer Anthony R. Wood at 610-761-8423 or email@example.com.
Inquirer staff writers Larry King, Bill Reed, and Amy Worden contributed to this article, which also contains information from staff reports.