Yes, chilly and misty is definitely atypical in late September! My b'day is 9/29, and I'm a So Cal native; my very clear memory of almost every single b'day (39 spent here) is of days in the range of 85-95. Can be hotter, but usually not; what is more likely is the winds that make it very, very dry. However, as is usual for CA all year round, it cools down very nicely at night!