Yes, internal variability is chaotic motion. However, we can technically predict internal variability, just like we can predict the internal variability of a coin flip over many flips:  roughly half heads or tails.  I think what you are asking is whether we can *deterministically* make predictions in the face of internal variability.  Can we say that next flip will be heads?  or will it be tails?  That’s a lot harder and you’re asking a question about predictability. We have another blog post on this topic…

https://www.climate.gov/news-features/blogs/enso/what-predictability