Thank you for your question! It's difficult for me to see a clear connection between this triple-dip La Nina and the frequent western U.S. atmospheric rivers. As we discussed in this post, La Nina typically causes a reduction rather than increase in western U.S. atmospheric river activity. The increase this year has been associated with an extension of the jet stream into the Southwest, which we typically do not see during La Nina, and I do not see how the "triple-dip" classification would change that. 

One of the main points of this post is that it's difficult to rule out the role of chaotic atmospheric variability that is unrelated to the underlying sea surface temperatures when it comes to unusual Southwest U.S. precipitation. However, we still need more analysis to see if the particular sea surface temperature pattern this year played some role, including the unusual frequency of atmospheric rivers. If there aren't any climate researchers looking into this now, I'm sure there will be some soon!