January in Istanbul is the rainiest and the coldest month of the year. In January, the weather in Istanbul is typically cold. Average daily high temperature in January is about 8 degrees above zero. On average, Istanbul has 17 rainy, 7 sunny, 6 partly cloudy, and 1 cloudy day in January. The rains are usually moderate. January as well as February and December is considered the most uncomfortable time to visit Istanbul.