You were told correctly. They work much better in low humidity.I am told that "evaporative" generally don't operate satisfactorily here because of the high humidity.
For those that are curious: an evaporative cooler has pads all around the outside. A water pump wets the pads. The fan inside then blows the cooled air into the house.
There can be as much as a 25F (14c)difference from outside to inside.

. Originally the gig was last September on a Saturday, on that day were in Yorkshire for a family birthday tea, we were then going to move on to Sheffield but The Who cancelled and changed to today so we finished work at 12.30, pub for a light lunch then set off later 
By the fifth shower were you still able to find any bubbles ??