I goofed when I identified this last year. It is a male Slaty Skimmer, Libellula incesta. A Bar-winged Skimmer would have noticeable black bars extending out from the thorax near the middle of the wings. This one doesn't.

Libellula axilena. This one doesn't have much in the way of black bars on the wings, but they vary. The dark blue abdomen with lighter blue on the top of the thorax and base of the abdomen suggests Bar-winged rather than Slaty Skimmer. I can also just barely make out the whitish area near the base of the hind wings. This one sure has beat-up wings, but that's consistent with the late August date.