I live at the foot of the foothills in Central Valley Cali. June, July and August are often 100+ degrees. Riders tend to get out early in the morning to beat the heat and get better air quality. I wouldn't say people here do less mileage than elsewhere. You just adjust your riding habits. Luckily, we have a dry heat with little humidity. When someone says they were "toast" on a ride, they often sort of mean it.

Anyway, ocean breezes and 80's weather would be sweet, but you'd be surprised what's "do-able" with weather. (You know, that LHT does have 3 bottle mounts...you might use them all!) It'll be fine.