We hosted a large gathering of SB folks last Fall. We did some local shore diving, Wreck Alley, the Coronados (Baja Norte), Channel Islands and a multi-day stay on Catalina which included both shore diving and boat dives. It was a huge success.
...and yes, the weather in the Fall is gorgeous here. The only potential concern is that the cyclonic activity in the Southern hemisphere and Tropics is peaking and pumping out solid ground swell energy. So shore diving at South facing can be iffy due to large surf. No worries, there are plenty of other options.