I have closely tracked RH and quality for 2 years now. I have both an analog hygrometer and a recording temp/humidity unit in my shop and I can definitely see a difference from a bone dry desert day to a muggy "SW desert monsoon" day. One of our muggy days is probably considered nice and dry to you folks on the gulf!
Swirling/shaking IS something we can control and is a REALLY wild variable in the mix of getting good acceptable coats with BBDT.