July in Blenheim is 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 16 sunny, 10 partly cloudy, 4 rainy, and 1 cloudy day in July. The rains are usually moderate. July as well as June, August, and September is considered the most uncomfortable time to visit Blenheim.