In August, the weather in Pematangsiantar is typically hot. Average daily high temperature in August is about 28 degrees above zero. On average, Pematangsiantar has 29 rainy, 1 sunny, and 1 cloudy day in August. The rains are usually heavy. August as well as January, February, March, and April is considered the most uncomfortable time to visit Pematangsiantar.