Generally the best time to travel to Hawaii/Kona would be off season in the spring - late February to May (excluding Easter & spring break) and fall - Oct to early December (excluding Thanksgiving)
BTW, humpback whale watching season (Kona) is mid January to early March.
And you don’t have to take a cruise to see them ether, just look to the shore and watch for the plumes of water.
AA, AS, DL, UA all have LAX-KOA non-stops