Hi,
@Tedbow00. Welcome to NGA from one fellow Houstonian to another! I have a bunch of adeniums as well. As for the issue, ditto on what Rick said, only to add that this needs to be done ASAP. If it is rot, it spreads extremely quickly and the sooner you can get it out of the pot and any rotted parts cut off the better. Also, if you cut any roots off that might have rot you'll need to leave the plant unpotted for at least several days to a week so that the newly cut roots can dry and callous over - otherwise, you are just inviting rot back in if you stick freshly cut roots directly back in soil.
When you repot, make sure to use very well draining soil. You can use any regular potting soil mixed with extra perlite at a soil:perlite ratio of 1:1 or 3:2. In your case, I'd go 1:1 (50% soil/50% perlite).
Our rain has been crazy the last couple of years, hasn't it?? Our springs and summers have been either feast or famine in regards to precipitation. Luckily my adeniums weren't adversely affected by the rain, but they were all in full growth at the time, so that is not doubt what saved them. I had recently trimmed a few of them, but they had popped new buds by the time the rain hit.
Good luck - let us know the results and definitely ask if you have any other questions or need any additional advice!
Carter.
