Original Post
I'm the developer of Physical Water Surface, an ocean material for Unreal Engine 4 based on Gerstner Waves. One of the most requested features was to implement seamless transitions between different sea states. It took some time, but I think the results speak for themselves. You can see the transitions in this video:
During a transition, I gradually update the wave parameters each frame in such a way that the change in sea state is completely smooth. The algorithm takes into account the position of the camera, making sure that be transition looks good from the point of view of the player. Please let me know what you think about my implementation! I've developed the transition algorithm myself and would like to hear how it compares to what other people have done.