Hainan is the southmost province of China and lies at the same height as Vietnam. A tropical region you could say an no one built heatings into houses and appartments.
Last winter was my first to live in Haikou and I can tell you that never in my life I had it this cold before.
First of all naturally I was not really prepared for a “winter” on an tropical island. All my wintercloths are still in Europe. We had temperatures around 6°-8°C. Now you may think “hey what is this guy complaining about?” but please take into account that the outer temperature equals more or less to the temperature in my appartment! The cold really creeps into your body step by step … some days I spent more or less in my bed, the only warm place 😉
This was before the chinese Spring Festival a month ago.
During the last day we had 34°C. A real change from winter to sommer within 4 week.

Haikou beach in Winter