It's humid where I live, too, but not especially so--not that awful degree humidity you have on the east coast. But it is very hot and unremittingly so in summer. My storebought juices spent the entire season last year out of direct sunlight but in temperatures between 75 and 90 degrees F (usually 82, though) and seemed none the worse for it.
I have nothing to compare my experience to, ie, i dunno what they would have been like if they'd been in the fridge or ac, but I thought I'd just put that out there.