The Brief Scattered showers will move across the Philadelphia area on Wednesday. Temperatures will return to the 90s on Thursday, leading to the sixth heat wave of the summer. Humidity will rise on Wednesday as scattered showers sweep across the region, leading to the sixth heat wave of the summer. What we know:Forecasters say showers will continue off and on throughout the day in scattered parts of the Philadelphia area. The National Weather Service has issued a flash flood warning for parts of the Philadelphia area until 5:30 p.m.