No one has mentioned "gale" A strong wind about 40 mph with rough seas. A gale is Force 8 on the Beaufort scale.

If you want to talk about the waves being big, you can say “rough seas.” If you want to talk about it being windy and rainy, you can use general-purpose terms like “storm,” or you can also use some terms that are sea-related like “squall” (a sudden storm) or “tempest” (an old-fashioned word for storm that is often used in relation to the sea)>.

...or how about 'choppy'? If the sea is choppy, it's rough with small waves.

ominous, treacherous, torrential, apocalyptic. just a few adjectives that might be useful :) ominous sky treacherous waves torrential downpour apocalyptic winds