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The Tonga humpback season runs from roughly July to October, and September sits at the tail end of it. Plenty of people assume that means the best of it is over. In practice, September has a character of its own, and many repeat visitors prefer it. Here is what the whales are doing in September, how the water feels, and what that means for a whale swim in Tonga.
Humpbacks arrive in Tongan waters after feeding in the Southern Ocean, and the first wave is mostly males, followed by mothers who give birth in the warm shallows. By September the calves are a few weeks to a few months old and much bigger than the newborns you see in July. They are stronger swimmers, more curious, and they spend a lot of time practising tail slaps, small breaches and flipper waves near their mothers.
For swimmers, this often means livelier encounters. A calf that is a bit older will swing around and come close to look at the boat, while its mother stays between you and the open water, relaxed and watchful. You will also see competition pods, where several males chase a female, but those are mostly seen earlier in the season. Our post on humpback whale behavior explains what you are looking at when you see each type of group.
In September the water around Tongatapu sits at roughly 23 to 25 degrees Celsius. That is comfortable for a long float, but it is not bathwater, and you will cool down after thirty minutes of drifting still. A 3 to 5 millimetre wetsuit is the standard choice, and a hood or rash guard under the suit helps if you get cold easily. Our trip includes a wetsuit, mask and fins, so you only need to bring your own if you prefer a custom fit.
Air temperatures are mild, with sun and trade winds. Mornings can feel cool on the boat, so bring a light windbreaker. Seas are not always flat in September, and some days there is a swell. If you get motion sick, take something before you leave the dock.
Tongan rules limit the number of swimmers who can be in the water with a whale at once, and the guide controls the timing. The boat stays back, you wait for the signal, then four people slip in quietly and float on the surface. You keep still and let the whale decide. Sometimes a mother and calf stay for half an hour, and sometimes they leave after a few minutes. Every encounter is different, and this is why a full week of days on the water gives you far better odds than a single day trip. We walk through a full day in a humpback swim day in Tonga, hour by hour.
Vava'u gets most of the attention and most of the boats. Tongatapu, where you land in Nuku'alofa, has only a handful of licensed operators, which makes September even more relaxed. You are less likely to queue behind other boats, and the whales are often calmer because they are not being approached all day. If you want to compare the islands, our guide to Vava'u vs Ha'apai vs Tongatapu goes through each one. For the wider seasonal picture, see the best time to swim with humpback whales in Tonga.
You need to be comfortable in open water, but you do not need to swim fast. Most of the time you float, breathe through a snorkel and watch. The effort comes in short bursts when the guide asks you to move toward the whale or away from it. Practise snorkeling with fins at home beforehand if you can, and be honest with the guide about your comfort level. It is snorkeling only in Tonga, with no scuba or freediving near the whales. If cost is on your mind, we break it down in what it costs to swim with humpback whales in Tonga.
September works well if you like active calves, a calmer scene and slightly lower prices than the peak weeks. The trade-off is that the whales are starting to head south by the end of October, so the later you go, the more the odds depend on luck. A trip in the middle of September, with several full days on the water, is a safe place to be.
Our Whales of Tonga expedition runs from 17 to 24 September 2027, with a maximum of eight guests and a private boat for five whale days. It includes seven nights, all meals, airport transfers and your wetsuit, mask and fins, plus photos and videos of the group. It also combines nicely with our Fiji expedition, which starts the day after. Have a look at the Whales of Tonga expedition page for the full plan and availability.
