NavList:

David Burch pointed me in the direction of some good references.   I'm going to do some reading and thinking and report back.   I think the Gulf Stream is a good example to work from, since we have reports that distinctly show the steepening of waves coming from the north.  I've seen this steepening in tidal flows in other situations (some a bit hairy).   

I think already the current gradient effect of focusing the waves that Frank mentioned is one distinct culprit, but I don't quite understand how this would steepen them, although I could be convinced.   I'll let you know what I find out.

John H.