August is hot. And Humid. Depending on where you live, that may be true whether you go on a Cruise or not.
But if you go on a cruise, the ship will provide an ocean breeze, shade, loungers, pools, A/C cabins bars, restaurants and common areas to get a relief from that heat. Plus plenty of cool drinks, alcoholic or non. So on balance, I'd rather be on a cruise ship in August instead of somewhere else in August.
We went to the Western Caribbean in late August. Yes it was hot. But it was also wonderful.