November to February is Sanya's golden season — temperatures hold steady at 22-28°C, and the sea stays around 25°C, warm enough to swim. When the north is buried in three layers of down, a T-shirt and light jacket will do all day here. One caveat: late December through early January is peak peak season, with flights and hotels running roughly 3x low-season rates. If your schedule is flexible, November or mid-to-late February offer far better value.
For clothing: summer wear by day, a light long-sleeve for mornings and evenings. Don't skimp on high-SPF sunscreen — Sanya's winter UV is still fierce, and you can burn even on overcast days. A long-sleeve rash guard for swimming doubles as sun and jellyfish protection. Footwear: slip-resistant sandals plus a pair of sneakers cover almost every scenario.
Winter is also Sanya's best season for diving and boat trips — visibility is high and seas are calm. The underwater worlds of Wuzhizhou Island and West Island are at their most beautiful now. The only downside is peak-season queues at attractions. For hotspots like Nanshan Temple and Wuzhizhou, arrive before 8am to beat the tour-bus rush that hits after 9.