A flash flood watch is in effect through 5 a.m. Thursday in Philadelphia and the surrounding counties in Southeastern Pennsylvania.
The National Weather Service says that with 9 to 11 inches of rain falling parts of the metropolitan area so far this month, September is already in the top 5 list of wettest Septembers on record.
The watch means that heavy rains could develop, creating flash flooding in some areas.
Should those conditions become likely, the watch could be upgraded to a more serious flash flood warning.
There is chance of showers and thunderstorms in the forecast through Friday.