That's also average sea level. If hurricanes get more powerful or more frequent, then you're going to want to account for the storm surge as well.
[1] https://www.wsj.com/articles/the-hurricane-lull-couldnt-last...
"More thoughtful and effective disaster policies are needed because the future will bring many more weather disasters like Hurricane Harvey, with larger impacts than those of the recent past." (From your own link)