January in Pematangsiantar is the rainiest and the cloudiest month of the year. In January, the weather in Pematangsiantar is typically warm. Average daily high temperature in January is about 26 degrees above zero. On average, Pematangsiantar has 31 rainy days in January. The rains are usually heavy. January as well as February, March, April, and May is considered the most uncomfortable time to visit Pematangsiantar.