Our only visit was in October, so I have no other point of reference, but the weather was perfect at Aulani the whole time. It was a bit rainy on the North Shore day and our Kualoa Ranch day. The water was very rough on the North Shore - no swimming, but there were some serious surfers. The water was perfect in the lagoon at Aulani and was also very calm in Waikiki. As for crowds, while no where we went was empty, it wasn't slammed either. We went on our school's fall break, which overlapped a bit with Hawaiian schools' fall break that year. The weekend was busier at Aulani. We used those days to tour the island, so we were only at the resort in the evenings.