Most pianos has a heater rod installed, make sure to keep it turned on. If your piano is in a room that is not too big, you can use a room dehumidifer. Novita has a few good models for that.
You can also place a few thirsty hippo inside your piano.
Actually, slightly higher but constant humidities does not hurt your piano as much as highly fluctuating humidity. So, you should try to keep the humidity in room constant.
Pianos can also be "prepared" for wet climate. Usually pianos that are destined for asia market already are prepared for wet climate. If you are buying an European piano, then you can speak to the dealer and ask the manufacturer to prepare it accordingly.
Hi waiyean, thanks for the reply and advice. my piano is a new Kawai upright, comes with the heater rod. I’m planning to move it to living room next year when i move to new house – and i can no longer afford the option of "24x7" aircon.
The sales lady from Robert Piano suggested to use full-height cover to block out certain humidity. I think I will go for that once I turn off the aircon, maybe with a few Thirsty Hippos in the piano.