The water is flat, you can either kite on the offshore side of the island or onshore. There is reef on the offshore side of the island creating a big lagoon. It is best at high tide. You can sail over it, it is about chest deep.
Best and usual direction is SE. The wind is steady. The wind is best from mid June to September. The wind is consistent. This is in the trade wind zone and blows 15-18 knots in the afternoons. Works in all directions.
You have to fly to the main island in Tonga, then to the Haapai group. You can stay Pangai (Lifuka Island) and get a ride to the beach daily. There you need to sail across the estuary on the kite and end up at the lovely beach. The island is only accessible by boat.
Only rule is do not hit the humpback whales, they are beautiful. The local people love you jumping over their boats. Bring drinks and food, nothing available on the island.