What's up, Supina?

Ok, so I've been focused on the front lawn and haven't said much about the backyard in some time. That's because I don't have a clue what's going on back there, but it sure doesn't look good and it seems to only be getting worse. The following photos show the progression.

Here are some shots from 7/26:

A closer shot of a patch that appears to be dying

And some from 9/1:

It's not a pretty sight. I just wish I knew what was wrong.

This is what I do "know":

1. It doesn't appear to be a fertilization issue. Not long after the first set of shots from July I gave some fertilizer to two small areas of the lawn and it didn't seem to make any difference.
2. I've also been keeping it well irrigated, watering roughly every other day or so. That said, we haven't had much rain since late June.
3. The summer hasn't been particularly hot (unlike last summer). There was a hot stretch in mid-July (7/14 - 7/19) with highs in the low 90s, and also the end of August (8/19 - 8/31).
4. There are some areas that seem to be fairing better than others - why?
5. From what I can tell (which is next to nothing), it doesn't appear to be a disease.

My best theory at this point is that it's simply the heat since supina bluegrass doesn't like it hot. This theory will soon be tested as fall arrives, at which point I'm very much hoping it will spring back to life. At this point since I don't have a clue what to do about it, I'm just going to wait it out and see what happens.

I think it goes without saying that my "experiment" idea is off for this year, which is just as well since I'd barely have the time for such a project.