It sounds like your hibiscus have a bacterial or fungal leaf spot and the clue is that you are noticing the damage now while the weather is still cool and wet. The good news is that these leaf diseases will usually disappear when the rains stop and unlike black spot on roses these infections do not ruin the general health of the plant. The best control is to collect the fallen leaves and pull off any infected leaves on the plant. This will stop the spread of the spores. Try to keep the foliage as dry as possible as moisture spreads the disease. Some varieties of hibiscus are more susceptible than others to leaf spot. If you cannot tolerate spring leaf spot you may want to replace your Hawaiian Sunset Hibiscus with another variety. Research has shown that spraying a fungicide to control hibiscus leaf spot is not effective because the damage is so seasonal. Summer is coming - I think you'll see less spots soon. Keep growing, Marianne Binetti