Candy Making.

[sexobon]

That was interesting buster. Multiple references to it popped up when I Googled "making candy in high humidity" and they all say about the same thing:

CraftyBaking.com

1. Barometric pressure and humidity greatly affect candymaking: My advice is to never make candy on a humid day!
• Many people dismiss the effect of relative humidity in the air because it's hard to feel or see the difference between, say 50% and 25%. But the difference is dramatic. If the relative humidity is above 35% (give or take) the breakdown of the sugar begins before it is even cold to the touch. That stickiness you feel on the surface of the hardened sugar is the same that keeps it stuck to the mold. Either a) the room should be air-conditioned and have a dehumidifier, or b) it should be a dry winter day. ...