December in Nantucket is the rainiest and the cloudiest month of the year. In December, the weather in Nantucket is typically cold. Average daily high temperature in December is about 7 degrees above zero. On average, Nantucket has 14 rainy, 7 sunny, 5 cloudy, and 5 partly cloudy days in December. The rains are usually heavy. December as well as January, February, and March is considered the most uncomfortable time to visit Nantucket.