The swollen Susquehanna River is expected to reach about 26.5 feet by Friday evening, after reaching about 25 feet in Harrisburg overnight, the Pittsburgh Post-Gazette reported.
Forecasters at the National Weather Service had predicted that the river would crest around 29 feet.
Water already began spilling over the banks in low-lying areas in the state. More than 1,200 National Guard troops are on flood duty in the state.
Officials have confirmed five deaths so far from the flash flooding to include an 8-year-old Lancaster County boy who was swept off his feet by rushing water.
The flooding is occuring because of remnants from Tropical Storm Lee that have been lingering in the northeast since Wednesday.
Take a look at the rescue efforts and flood damage below.