Het weer in Sanya (Hainan) in december

Forum posters describe the first half of September in Sanya as genuinely stuffy - high humidity, little wind unless a typhoon is nearby, and rain most nights - while mid-September onward is generally rated as fully fine, with sunnier days and just occasional rain or thunderstorms. Posters are consistent that September sits within Hainan's official wet season (June through October), with real typhoon risk that increases the later into the season a visit falls. Posters specifically recommend late September and October, alongside April and early May, as the best overall windows, given the improving weather and easing typhoon risk as the month progresses. Posters generally rate September as a mixed month for Sanya - genuinely humid and typhoon-prone early on, meaningfully better by the back half.

Forum posters call March genuinely nice - already warm but not yet properly hot, with temperatures generally in the 25-32C range and around 30C reported by month's end. Rain is possible on occasion but not a constant feature, so posters recommend packing rain gear as a precaution rather than an expectation. March sits within Sanya's October-to-March peak season, meaning good weather comes paired with higher hotel, flight and cruise prices than the shoulder months. Posters describe swimming as comfortable essentially year-round here (sea temperatures rarely drop far below 25C even in the cooler months), making March a strong pick for beach time without the year's hottest, most humid stretch.