July in Blenheim is the sunniest and the coldest month of the year. In July, the weather in Blenheim is typically warm. Average daily high temperature in July is about 10 degrees above zero. On average, Blenheim has 11 rainy, 11 sunny, 6 partly cloudy, and 3 cloudy days in July. The rains are usually heavy. July as well as May, June, August, and September is considered the most uncomfortable time to visit Blenheim.