Altocumulus castellanus clouds on top of the ocean, also there are stratocumulus lenticularis clouds under them, there was convective activity going on at the time (various cumulonimbus clouds in the distance)
<a href="//commons.wikimedia.org/wiki/User:Couch-scratching-cats" class="mw-redirect" title="User:Couch-scratching-cats">Couch-scratching-cats</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>