Victoria, one of the most important aspects of growing plumeria in pots is to make absolutely certain that the potting media is extremely well draining and that the pots' drainage hole are large and open. If you've got these two things in place, I sure wouldn't be worried about rain. Of course, I am assuming that the plants are getting lots of full sun. I've got 400+ potted plumeria, every single one outside and in sun, at least 6 hr. of sun. This is our rainy season, and it's not unusual to get rain almost every day for a week or more at a time. A week ago we got over 6" over a 4 day period. Plumeria are sun and water loving plants. But they don't like "wet feet".
