Thanks so much for posting your photos! I was fortunate enough to dive with humpbacks once, but didn't have a camera, so these are a wonderful reminder
My experience was in Niue, about 600 km NE of Tongatapu or 400 KM NE of Vava'u. I was there for work, it was a Friday afternoon, and I had the next day free, so I went to the local dive shop which was the garage of the divemaster's house and asked about going out the next day. He looked me over, and said, "How about now?". Well, it was not long before sunset and I knew I would only be in Niue once, so I explained that I wanted to spend a whole day in good light. He motioned for me to follow him out to the cliff edge, then just stood there looking out to sea. I was beginning to think that I didn't want to dive with a nutter, and was about to make my excuses, when a humpback breached right below us, 50 m offshore. The guy turned toward me, raised an eyebrow, and asked, "So is now good?". I didn't need to be asked a third time. After a frantic 10 minutes to gear up and get into a zodiac, we were in the water with a cow and calf, and another nearby. The whales were not at all spooked, allowing us to get within perhaps 10 m, and spent nearly an hour circling us near the surface. We only got out when it was too dark to see. As we motored back in, one of them breached again. What a spectacular dive and spectacular send off!
By the way, the rest of the diving in Niue was also great. The island is a raised atoll with the nearest land being the Tonga islands, so it attracts a lot of species. Visibility seems endless. A key feature is the sea caves cut into the cliff faces, some with collapsed roofs with sunlight streaming in from the landward end. Everywhere there are lots of sea snakes and morays and lobsters and swarms of pelagics out at the reef edge, and the most pristine coral I've seen. It takes some doing to get there, but its well worth the trip.
Anyway, thanks for sharing your photos and triggering those great memories!