Het weer in Vava'u (Vavau) in mei

There isn't much March-specific detail for Vava'u on the forum, but the broader Tonga threads are useful context: posters consistently described April through August as the cool, dry, less humid stretch of the year, which by contrast puts March still inside the warmer, wetter season with a real chance of thunderstorms and heavy rain. One older thread mentioned March flight disruptions between the islands, a reminder that inter-island travel here can be weather-dependent this time of year. June/July got repeated mentions as the more reliably settled alternative.

Forum posters consistently name July through October as Tonga's best window overall, coinciding with whale-watching season and generally good weather - September sits comfortably within that stretch. Posters describe real day-to-day variability even during a good week: one detailed trip report logged mostly pleasant weather across ten days on the water, with just one day of heavy rain, one of light rain, and a couple of days with 3-6 foot swells. Posters note ocean water temperatures drop noticeably during these winter months, though Vava'u itself runs a bit warmer than more southern parts of Tonga. Posters generally recommend September specifically for whale swimming, with fewer crowds and good conditions reported compared to peak-season months.