It looks fungal. Cucurbits and any plant with gray green fuzzy leaves are designed for places that don't rain a lot. It is best not to plant in the exact same spot but some fungal spores will hang around awhile and they are in the air and on plant residues. Some can even be on the seeds.
When you plant squash or cucumbers wait until the weather has sufficiently warmed up. To prevent splashing on the leaves use a drip system and mulch to help with the splashing. Make sure the plants get good air circulation around them and trellis them up if you can. If the weather turns wet and humid, proactively start a fungicide program. Neem or horticultural oil will work to help water wick off the leaves. Sulfur can also be used but you cannot use sulfur and and oil together or they will burn the plants. Other things help like baking soda as a dessicant and milk spray which changes the pH and coats the leaves to make it more inhospitable to fungal problems. You have to repeat sprays every 3-7 days while the weather conditions persist. Ultimately all of my cucurbits end up succumbing to fungal disease, but I usually get a decent crop anyway. If it rains every few days, it is hard to keep the fungal disease away even with preventive sprays.
Happy gardening in Hawaii. Gardens are where people grow.