In the end of March the island is green and the wild flowers are blooming. It is beautiful.
Like everywhere we can have wind, rain and un-seasonably cold weather, make sure you bring clothes to handle this.
To see the current weather and temperatures check out the following link. Current weather on Catalina Island.
The water in the Pacific is salty, this has an advantage as you will have more flotation, and it also has a disadvantage and that is the possibility for chafing during the race. Make sure you prepare areas that rub so you enjoy both the beginning and the end of the race.