Gov. Tom Corbett declared a statewide disaster emergency ahead of the storm.
Flooding, power outages and sustained high winds are anticipated, his office said. Sandy could even bring snow to parts of southwestern Pennsylvania and in higher elevations.
"Essentially, this is a hurricane wrapped in a nor'easter," Corbett said.
Throughout the state, 1,600 National Guard troops were deployed, the governor said in a Twitter post.
Public schools in Philadelphia were closed Monday. Public transportation in the Philadelphia area has also been suspended.
The Rhode Island Emergency Management Agency urged all residents to prepare for prolonged power outages, wind damage and water damage by keeping an emergency kit, securing property and taking boats out of the water.
State authorities have taken precautions such as checking and clearing drains in flood-prone areas and relocating state equipment if necessary.
Public schools in Providence, the state capital, were closed Monday.
Obama has declared a state of emergency for Rhode Island.
Heavy rains from the fringes of Sandy pelted much of South Carolina's coast, from Charleston to Myrtle Beach.
Virginia was one of several states to declare a state of emergency ahead of the storm. Computer models predict parts of the state could see as much as a foot of rain.
Gov. Bob McDonnell said Monday morning that his state had seen signs of the storm for days, but the worst was yet to come. He asked for a federal emergency declaration, which would free up funding.
Sandbags piled up inside restaurants in the Old Town section of Alexandria along the banks of the Potomac River.
All public schools in Fairfax County, a large school district in northern Virginia, will be closed Monday and Tuesday. Schools in Arlington, Norfolk and Newport were closed Monday.