Happy Tolkien Day!
About the significance of the Great Wave
Letter #163:
I say this about the 'heart', for I have what some might call an Atlantis complex. Possibly inherited, though my parents died too young for me to know such things about them, and too young to transfer such things by words. Inherited from me (I suppose) by one only of my children, [note: Tolkien's second son Michael.] though I did not know that about my son until recently, and he did not know it about me. I mean the terrible recurrent dream (beginning with memory) of the Great Wave, towering up, and coming in ineluctably over the trees and green fields. (I bequeathed it to Faramir.) I don't think I have had it since I wrote the 'Downfall of Númenor' as the last of the legends of the First and Second Age."
Letter #180:
Out of that came the 'missing link': the 'Downfall of Númenor', releasing some hidden 'complex'. For when Faramir speaks of his private vision of the Great Wave, he speaks for me. That vision and dream has been ever with me - and has been inherited (as I only discovered recently) by one of my children [Michael].
I find this fascinating for we hear Faramir talk about the dream too with Eowyn and we have a whole country island perishing in a wave (Numenor). So yes, Tolkien does have an obsession with the Great Wave.