Information provided here can be applied to most any part of the country taking into account your own weather patterns.
In Florida, our rainy season normally comes to an end in September with the exception of tropical activity which is totally unpredictable. Your plumeria which has been exposed to almost daily rain during the summer is now going to become stressed by the lack of water if you do not supplement mother nature. Examples of this will be, lower leaves turning yellow literally overnight Days are now becoming noticeably shorter and there is less energy available to the plant so leaf yellowing is a normal part of their life cycle. However, letting the plants become dry all of a sudden will speed this process up considerably.
Dry hot humid times after the rainy season are the worst for rust on plumeria. We have found that regular dousing of the leaves every few days with water will slow the rust problem down considerably. It seems to rinse the spores off of the leaves. Try this and you will be amazed.
As the days continue to get shorter your plumeria will have less energy to work with and dormancy will take place no later than December and in some cases earlier, especially in northern climes of course. Once the tree has gone dormant it needs no water until spring. You may give it some while dormant just to keep the soil from becoming too dry to absorb water.
We will update later as we move toward winter. Try these suggestions, you will be amazed at the results.