Your soil looks very coarse. Are you planting in the same soil and what kind of fertilizer did you use? Onions do better for me in a soil that is more neutral to alkaline and while they need nitrogen in the beginning, when it is time to bulb up you have to stop the nitrogen and give it more bone meal. Not enough nitrogen in the beginning and you won't get enough green growth. Too much nitrogen when bulbing up, you won't get bulbs.
Onion leaves will start to yellow when it is near time for them to be harvested. Wait until all the tops have fallen. Usually the bulb will be poking up on top by now.
Happy gardening in Hawaii. Gardens are where people grow.