August in Hillsboro is the hottest month of the year. In August, the weather in Hillsboro is typically hot. Average daily high temperature in August is about 34 degrees above zero. On average, Hillsboro has 18 sunny, 9 partly cloudy, and 4 rainy days in August. The rains are usually moderate. August as well as January, June, July, and December is considered the most uncomfortable time to visit Hillsboro.