If you bring a stringed instrument from a manufacturer in the United States or Northern Europe, it will have been made in a climate controlled shop with the relative humidity of around 45 – 50%. But in the tropics, the relative humidity (RH) is somewhere around 80%, or 100% if it is raining.

What happens to your guitar? The soundboard soaks up humidity like a sponge, and like all wood, it expands. But its movement is restricted by the sides, which are glued to the soundboard at around a 90 degree angle. So it expands out away from the back. It distorts up or “bellies up” behind the bridge and collapses in at the sound hole due to string tension.

This happens gradually and the action gradually gets too high to be playable. Then the bridge pulls loose because it no longer conforms to the shape of top. Often the distortion becomes permanent if allowed to stay in that distorted shape for too long. The top gets “set” in that shape and the cost of the repair is often way more expensive than the value of the guitar.

One reality about stringed instruments, is that they don’t react well to RH changes of more than around 25%. If you take a factory built guitar built in 45% RH to the desert, say maybe 20% RH or less, it doesn’t take long and it will start to crack. Bring it down here to the tropics and it “blows up”, as I like to say.