If you're hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in San Jose City: The hottest months are usually April and May with an average temp of 81°F, while the coldest months are January and February with an average of 77°F. The rainiest months in San Jose City are July, August, September, and June, with each month seeing an average of 16 inches of rainfall.