December in Galveston is the rainiest and the cloudiest month of the year. In December, the weather in Galveston is typically warm. Average daily high temperature in December is about 16 degrees above zero. On average, Galveston has 15 rainy, 9 sunny, 6 partly cloudy, and 1 cloudy day in December. The rains are usually moderate. December as well as July, August, and September is considered the most uncomfortable time to visit Galveston.