If you have been growing the tomatoes in the same spot every year. It might be a good idea to start with fresh media and clean and soak the pots in a 10% bleach solution for 24 hours or more. Disinfect the area you were growing the plants in because spores can be on the ground and in the air for a while.
If you can, change to another location as far away as possible. If the weather turns wet or humid, use a preventive spray. Either Bayer 3 in 1 or homemade baking soda spray plus mineral oil. Only use one solution. Copper sulfate is the fungicide in 3 in 1 spray and sulfur and oil need a two week break or the plants will burn. Do a test spray on a small section of plant first.
If you are using baking soda spray. Make sure you spray within 3 days of the rain stopping. If it rains again you may have to reapply. I usually only have to spray when it is going to or has rained. If it is sunny every day and the leaves are not wet at night there is no need to spray.
https://gardening.about.com/od/gardenpro ... Mildew.htm
In case it is not a fungus, experiment with other tomatoes that have more disease resistance. If you can, plant something completely different. No solanaceous or plants that carry the same disease to eliminate host plants. Check plants nearby for insects reservoirs. Aphids, thrip, leaf hoppers are the usual suspects for transmitting diseases.
Learn how to read the signs:
https://erec.ifas.ufl.edu/tomato-scoutin ... ndex.shtml
Happy gardening in Hawaii. Gardens are where people grow.