On the island of Hainan, the southernmost province of China, the climate is almost tropical, with very mild winters, and long and hot, muggy and rainy summers. The average January temperature is in fact near 20 °C (68 °F) in the north, and slightly higher in the south. The rains are abundant from May to November on the eastern side, while the western side is more sheltered, and receives moderate rains only from June to October, and even abundant in August and September: therefore, the total annual rainfall hardly reaches 1,000 mm (40 in), not a lot for a tropical area, while on the eastern side of the island it rains about twice as much.

On the northern coast, where the capital Haikou is located, the average January temperature is 18 °C (64 °F). In winter, the north-east monsoon brings cloudy days when there are some drizzles, or fog can form. Sometimes cold and windy days can occur, with highs around 15 °C (59 °F) or even below. In January 1977 the temperature dropped to 3 °C (37.5 °F), while in January 2016 it dropped to 6 °C (43 °F). Here are the average temperatures.
Haikou - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)151619222425252524222016
Max (°C)212226303233333231282522
Min (°F)596166727577777775726861
Max (°F)707279869091919088827772

In Haikou, rainfall amounts to 1,600 millimeters (63 inches) per year, and is abundant from May to October.
Haikou - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)20355010518521021022525020095351625
Prec.(in)0.81.424.17.38.38.38.99.87.93.71.464
Days9111012161614151513108149

In Haikou, the sun shines about 2,000 hours per year: in winter the sky is often cloudy, while from May to September it shines a little more often than in the southern Chinese mainland.
Haikou - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours434677876654

The sea temperature is similar to that of Guangdong, although it is a bit warmer in winter. However, it is a bit cool for swimming from January to March, while it is pleasantly warm from May to October.
Haikou - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)212122242729292929282523
Temp (°F)707072758184848484827773

Yalong Bay, Sanya

On the southern coast, where the tourist resorts are found, the winter temperatures become milder, and the climate can be defined as tropical, in fact the January average is 22 °C (72 °F). However, from November to March sometimes the night temperature can drop to around 10 °C (50 °F). Here are the average temperatures of Sanya, the main city of the southern coast.
Sanya - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)182022242626262625232119
Max (°C)262729313232323131302827
Min (°F)646872757979797977737066
Max (°F)798184889090908888868281

Here the rains amount to 1,400 mm (55 in) a year; the trend is very similar to that of the north coast, but the period November-April is drier because this coast is sheltered from the north winds.
Sanya - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)1015204514020019522025023460101390
Prec.(in)0.40.60.81.85.57.97.78.79.89.22.40.454.7
Days344610141416171474111

In winter, on the southern coast the sun shines more often than on the northern one.
Sanya - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours656677767666

On the southern coast, the sea too is warmer in winter, so that the water temperature does not drop below 23 °C (73 °F) in January and February: after all, you can swim even in winter.
Sanya - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)232324262829293029282624
Temp (°F)737375798284848684827975

On this island, the interior is occupied by hills and mountains, where lush forests grow. The highest mountain is Wuzhishan (the "five finger mountain"), 1,840 meters (6,040 feet) high. On the top the daytime temperature is around 10 °C (50 °F) from December to February, and around 20 °C (68 °F) from May to September. However, access has recently been closed to foreign tourists.

Typhoons


Together with Southern China, Hainan can be hit by typhoons, tropical cyclones of Southeast Asia. Typically, typhoons occur in this area from June to mid-November, but sometimes (though very rarely) they have affected this area outside of this period, in April or in May.

When to go


If you want to go on excursions, you can choose the coolest period, from mid-November to late March.
For a beach holiday, you can choose the month of April (or even May, which however is warmer and rainier). The May-September period is hot and muggy, with showers and thunderstorms even strong, but also with some hours of sunshine. From June to mid-November, typhoons can occur, which bring strong winds and torrential rains.
On the southern coast (see Sanya) there can be days warm enough for sunbathing and swimming even in winter. On cool and cloudy days, you can go on excursions on the island.