That time of year the coast road has the least amount of traffic. So you can enjoy it. But it will not be all warm and toasty, it will be cool and probably a bit rainy.
If you are interested in the coast, probably going north is your best riding bet. If you want deserts, etc., then go inland to Joshua Tree, 29 Palms, Ocotillo Wells, the Agua Caliente hot springs on highway 2 south of Julian (a San Diego county park).