January in Jeju is the coldest month of the year. In January, the weather in Jeju is typically cold. Average daily high temperature in January is about 6 degrees above zero. On average, Jeju has 12 partly cloudy, 8 sunny, 7 rainy, and 4 cloudy days in January. The rains are usually moderate. January as well as February and December is considered the most uncomfortable time to visit Jeju.