If you're looking forward to lots of outings with your partner, check out these details about year-round temperatures in Hitachinaka: The hottest months are usually August and July with an average temp of 75°F, while the coldest months are January and February with an average of 44°F. The rainiest months in Hitachinaka are September, October, July, and June, with each month seeing an average of 8 inches of rainfall.