I googled tides pertaining to how the moon affects them. The main reason for that is because I am not entirely sure of how oceans would react to an additional object approaching the planet. I know, through the search on google and what wikipedia says, that if the moon were closer, tides would be stronger (or something to that effect). I would assume another object gradually getting closer would do the same.
However, would it affect how the seas would behave? As in, would waves crashing to the beach be far more volatile?
The main gist of what I'm trying to found out is this: The idea is that an extinction event sized asteroid is going to strike Earth. The story is less about the asteroid and more about the people deal with the inevitable end. The thought is that a couple try to finish some daring and exciting things before they die. One of which is surf potential stronger waves than anyone will have ever seen, thanks to the asteroid largely changing the ocean's behavior. Is this something viable? If not, I will have to retool the idea altogether. Not that it will be a bad thing, but it'll obviously take work.