If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Cerritos: The hottest months are usually September and August with an average temp of 65°F, while the coldest months are December and November with an average of 65°F. The rainiest months in Cerritos are April, May, October, and November, with each month seeing an average of 21 inches of rainfall.