July in Oamaru is the coldest month of the year. In July, the weather in Oamaru is typically cold. Average daily high temperature in July is about 9 degrees above zero. On average, Oamaru has 15 partly cloudy, 11 sunny, 3 rainy, and 2 cloudy days in July. The rains are usually light. July as well as May, June, August, and September is considered the most uncomfortable time to visit Oamaru.