It really looks like the pot is too small. It's a good idea to see if the plant is pot-bound.
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.
The pot may be too small, but from observing my Hibiscus I've noticed that leaves turn yellow like that quite often; I think it's just the normal life cycle of the leaves. Now, if they all start turning yellow....
The pot is small but I agree with John, the hibiscus looks healthy and the leaves are just sinescing. If you want the hibiscus to bush out more you can cut the top and propagate it to start another plant. Otherwise, the hibiscus is just likely to get taller but won't branch out much.
Happy gardening in Hawaii. Gardens are where people grow.
I yield to the more knowledgeable members -- I haven't had hibiscus for a while now -- so my memory and knowledge/info is no longer fresh
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.