Hot

Moral of the story:  too hot or too cold is bad,  too high or too low of humidity is bad.

 

Most hand-crafted guitars are made with hide glue or titebond.  Should there need to be a repair, both glues can be un-done by applying heat and moisture. This is a highly desirable trait.

So what happens to a guitar when it rains (high humidity) followed by several days of ~100F temperatures (hot).... and you don't have air conditioning?   This is highly undesirable.

A good idea would have been to de-tune them all to remove stress.

No major trama to report, just a little bit of glue separation on one guitar....

A quick bit of sanding (slide in a piece of sandpaper, push down softly, pull out sandpaper. Flip over and repeat), wick in some fresh glue, clamp.  Back to good-as-new.

Better idea:  bought a small window air-conditioner for those rare extra-hot days.

We already have humidifiers for the much-more-common-around-here cold and low humidity days that help prevent soundboard cracks.  

Interesting note:  one other thing that can happen in the hot-and-humid case is that joints can "slide".  I.e. the bridge might move forward slightly throwing off the tuning, or the fingerboard might move slightly throwing off the action.