Just like you say in English: "the people of the storm is a great people" [equally "are" in English, but think of "populus" as a "nation" or "tribe" also],* "the peoples of the storm are..."—if there is more than one people/tribe/nation
Sicut latinè dicas: "tempestatis populus est magnus populus."* et "tempestatis populi sunt...", si sunt plus quàm unus populus seu natio seu gens.
* Etiam latinè ut anglicè, nisi fallor, "tempestatis populus magni piscatores sunt".
* Also in Latin as in English, unless I'm mistaken, "the people/nation/tribe of the storm are great fishermen".
I'm writing in Latin hoping for correction, and not because I'm confident in how I express myself. Latinè scribo ut ab omnibus corrigar, non quod confidenter me exprimam.