Even when humidity isn't high I've had problems when spraying outside in very warm weather. The problem is condensation resulting from cold propellant from the rattle can (propellant acts like a refrigerant absorbing a huge amount of heat when it suddenly changes to a gaseous state) and even bringing the surface to be sprayed outside from an air conditioned house just before painting. Try shooting inside. Or you can allow your parts to heat up outside first and use an airbrush with compressor and water trap. Spraying the rattle can paint through a straw into an airbrush jar can also allow the propellant to outgas eliminating all those tiny air bubbles that show up on a wet painted surface. Hope this helps!