High humidity isn't much of a problem for acrylic paints, but could become a problem for oil based paints. There are a few things to consider before you start to use any paint in high humidity conditions.
1) The dry time will be longer. The extra humidity will keep the paint sticky for a longer period.
2) Thinner coats are required or risk sagging.
3) Make sure the surface itself is dry and free of dew. Start painting latter in the day if you have too or work in the sun for better drying of the paint film.
4) Watch out for bubbles forming under the paint film. This will indicate a "wet" surface that needs to dry out.
5) The cure time will be longer. So, the paint film could suffer damaged from rain for a longer period. Keep your eyes on the weather and stop painting 3-4 hours before any storms show up.