What is wrong with my Hibiscus tree when the leaves start turning yellow?
This is common with these plants, and there are several reasons this can happen. This article explains many of them and will help you decide which is likely for your plant: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
Hibiscus leaves are turning yellow and falling off. . . . what do I need to do? Thank you.
There are several reasons this can happen. This article explains many of them and will help you decide which is likely for your plant: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
Does hibiscus like bright sun?
Yes, hibiscus enjoys full sun. Here is more information that may help: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm
My hibiscus is losing its leaves after they turn yellow. It is in partical sun and I water about once per week.
I would be willing to bet that the plant has a pest infestation. Some pests, like thrips, aphids or mites, can be difficult to see with the naked eye. I would treat the plant with neem oil. This will kill any harmful pests on the plant without being a danger to people or pets in the yard. Here is more information on neem oil: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Just in case pests are not an issue, this article has many of the reasons a hibiscus turns yellow: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
My buds are falling off the plant while still closed. Temps are reaching 100+ and the wind is gusting to 45. Could this be the issue and should I water daily due to this heat? Should I move it to part shade?
These conditions would definitely have an adverse effect on your plant. Yes, in temps like this daily watering is a must, especially with wind factored in. This will dry out plants quickly. If at all possible, moving it to a more sheltered and partially shaded location would be better.
There is a black mold at the base of my Hibiscus plants. Is this mold and is it from too much water? Live in Hawaii and the plant receives about 10 hours of sun each day. The sprinkler system waters it for approx. 15 min. in early morning, 7 days per week.
Sooty mold is a fungus often brought about by pests, namely aphids or scale. I would try treating the plant with neem oil, which is effective for handling these pests and is also a fungicide. Here is more information that should help you: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
I have a hibiscus plant that has several buds, and they look as if they are dying. What would cause this and what could I do to help the plant bloom.
It likely needs some more fertilizer, especially phosphorus which helps with blooming. Use a "bloom booster" fertilizer or add some bone meal to the soil to help add some phosphorus.
As for the dying buds, it could be thrips. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-flowers-hibiscus-blossoms-falling-off-plant.htm