December in Oamaru is the rainiest month of the year. In December, the weather in Oamaru is typically warm. Average daily high temperature in December is about 16 degrees above zero. On average, Oamaru has 9 rainy, 8 cloudy, 7 sunny, and 7 partly cloudy days in December. The rains are usually moderate. December as well as May, June, July, and August is considered the most uncomfortable time to visit Oamaru.