May in Oamaru is the sunniest month of the year. In May, the weather in Oamaru is typically warm. Average daily high temperature in May is about 12 degrees above zero. On average, Oamaru has 14 partly cloudy, 11 sunny, 5 rainy, and 1 cloudy day in May. The rains are usually light. May as well as June, July, August, and September is considered the most uncomfortable time to visit Oamaru.