Don't worry about the umbrellas you guys are in for a treat, not too hot, not too cold. No rain, S to W wind forecast up to Thursday which is flat and fast, should have good sea breeze kick in after lunch each day.
Heard someone say that some boats are not doing the spin nats because they are worried about breaking the boat for the Nats, one of the guys at the club asked if you had considered spin nats to be held after the main nats in future years.