Wow. It almost sounds like they're trying to scam you into paying more for your certification. Yeah, boat dives are quite a luxurious way to get certified. But a miserable day is a miserable day. Boat or shore matters little if you're diving in the 20 foot range and the swell is up.
First off, I have my eyes on the same time window, because the wife and I are getting away for our birthdays to dive Catalina the exact same weekend. I watch the SoCal marine weather very carefully, and I can't find ANY reputable source for what the marine forecast will be like next weekend.
All I can think of to back up such a forecast is is long range hurricane tracking?
Neither CDIP nor NOAA are forecasting what's happening that far ahead in SoCal. About mid-week is as far as they go, and forecasts that far ahead are highly speculative. As for normal shore-bound weather, it looks about the same for the next 10 days in SoCal.
Furthermore, if the shore dives are skunked around OC, who's to say a boat dive would be any less miserable? You're not going to be diving deep, which means if there's any swell up, the surge and vis will be terrible anyway. Take 10 Dramamine and pray?
Sources:
http://www.ndbc.noaa.gov/data/Forecasts/FZUS56.KLOX.html (the LAST one on this page applies to near-shore)
http://cdip.ucsd.edu/themes/cdip?pb=1&r=7 (Select "forecast" instead of "nowcast" to see what's on the way)
http://www.nhc.noaa.gov/?epac (No hurricanes forecast with any certainty.)
