August in Philadelphia is the rainiest month of the year. In August, the weather in Philadelphia is typically hot. Average daily high temperature in August is about 30 degrees above zero. On average, Philadelphia has 16 rainy, 10 sunny, 4 partly cloudy, and 1 cloudy day in August. The rains are usually heavy. August as well as January, June, July, and December is considered the most uncomfortable time to visit Philadelphia.