I have done Sundancer 2 in September. The weather was awesome. It is the rainy season, but we had no rain at all. I think it mostly rains on the mainland. It was hot calm and clear. It is hurricane season especially later in September, so get great trip insurance. There are very rarely hurricanes in Belize, but they do happen at that time of the year. Sundancer 2 and Belize Aggressor will be anchored in the Atoll known as Lighthouse Reef within sight of each other every night. It is quarry calm inside the Atoll. All of the diving seems to be on the lee side or inside of the Atoll, so it is very calm on the surface. There are sites on both the lee and windward side of Turneffe. Turneffe is mostly in the lee of Lighthouse Reef, so it is not usually rough. The crossing can be rough, but the boat will stay out there for the week. Sundancer 2 is a MUCH bigger boat and probably handles the crossing better. It was calm when we crossed.