It's very common here in Northern California for August to be on the cool side and September to be much warmer. It's not completely unheard of to have the warm September spill into a few weeks into October for Indian Summer.
It's November 15 and the high temperature in Oakland today was 79 degrees Fahrenheit or 26 C. I have the air conditioner on in my stuffy little apartment.
It's mid November. I should be wearing sweaters by now and turning on the heater in the morning just so I can crawl out from under the covers. This is completely whack, as the young people are fond of saying.