According to the magicicada.org website, three species are possible in Sewanee:
Magicicada tredecim – Underside of abdomen is mostly light orange/caramel. These are the ones that call waaa-oo from the treetops.
Magicicada tredecassini – Underside of abdomen usually all black, or with faint orange lines.
Magicicada tredecula — Well-defined orange stripes across underside of abdomen.
This individual crashed into my head while I was watering the garden, so I brought him down with the water jet and did some catch-and-release identification: Magicicada tredecassini. The sound he was making seems to match that on the magicicada pages also.