Yellow leaves is also a sign of root rot from too much water.
If you are using a drip system 2-3 hours may not be enough. If you are using a sprinkler it may be too much.
How much to water is dependent on the plant and the type of soil you have. Water 4-6 inches deep. Check the soil after about 45 minutes of watering and recheck every 15 minutes or so after that. You will have to dig down with a trowel to see how long it takes to water that deep. Sandy soil will have to be watered more often but clay and organic soils will hold on to moisture longer. Water again when the soil is almost dry 4 inches deep.
If your soil is sandy or you live near the ocean, you have to water more and some plants will not be salt tolerant unless you can grow them in pots and you don't have salt spray.
The temperatures will be o.k. but the tomatoes have to be heat resistant or they will stop producing and drop flowers once the temps exceed 88 degrees. Cherry tomatoes are much more heat tolerant than larger tomatoes. In extreme heat you may have to water more than once a day, provide some shading, and mulch.
Tomatoes will tolerate a pH 7.0 but it does not like alkaline soils.
Unfortunately changing soil pH takes about 6 months using sulfur to lower it. It would actually be easier to Put the tomatoes in a large pot 20 inch pot or at least 18 gallons. A SIP pot would be better since watering will be even and easy to do, you just fill the reservoir. Use a good potting soil which will be balanced and side dress with tomato and vegetable food. To correct soil faster you would need to add 8 inches of peat moss + sulfur to the soil before you plant. The peat moss is acidic and is a good substrate for the roots to establish.
The yellowing of the leaves can be from too much water, or if water is keeping the leaves wet, then fungal disease. I take off the lowest leaves of my tomato plants if they are touching the soil and they are not needed.
To fix the garden in the long run, I suggest you get a soil test from your local extension service. The soil test will tell you what you need to do to correct pH and what fertilizer you need. It would also be a good idea to add organic matter to help hold moisture in the soil so water will go farther. Add at least 6 inches of blended compost about a month before you do the soil test.
Happy gardening in Hawaii. Gardens are where people grow.