Hey Newman and YZMatt,
In higher humidity climates (90% and above) our evaporative vests will not work as well as they would in a more dry climate. This is not to say they will not work, as we have many riders in Florida and high humidity climates that swear by our HyperKewl vests and accessories. As with the case of all products that rely on evaporation for cooling (vests, swamp coolers, etc.) they will not work as well in high humidity environments (90% and above) because there is too much moisture already in the air.
An alternative is our Phase Change Cooling Vests which do not rely on evaporation to provide cooling.
Many of our top athletes wearing our cooling products are wearing our 4531 Elite Hybrid Cooling Vest as this provides both Evaporative Cooling and Phase Change Cooling. These vests are worn by the Honda International MX Team, The Kawasaki Monster Energy Australian Team as well as Tour De France Champion Alberto Contador and Formula 1 and Nascar Drivers.