I just noticed these gouges on the rear driver side tires. Should I be worried about a possible blowout? Should I replace them?
I don't think you need to worry about a blowout as you don't have any cords showing. This is slightly subjective, though, as you don't know what kind of damage was done to the sidewall from the inside. It looks as these tires are pretty worn in the first place, though. You may think about getting new ones anyway. Also, see about getting the rim trued when you do, as that dent in the lip cannot be doing you any favors (probably feels like the tire is out of balance).