It’s usually cuz when a hurricane makes landfall, and continues into more land. Obviously there isn’t any heat or water vapor inland so it weakens rapidly. But it kinda breaks apart which makes a giant wave like storm as seen in radars.
Hurricane debbie (S**TTY NAME EWW) already f**ked up the big bend (area where helene also hit) so helene being a low end cat 4 just worsened the damaged debbie already caused.