There's a good little hill in the first 0.5 miles that you do only once (you come down it right before finishing). Then most of the run on the south side of the river is relatively flat (gentle rollers). There's a short steep kicker right before you cross the river on Veteran's bridge. Then the north side of the river is where the hurt comes. Barton Ave is a big climb, and there are 3 more hills over there. So for 6-7 miles you're going up or down and it wears on the legs. Then come back across the river on the pedestrian bridge and repeat, so the last 5 miles of the race includes those 4 good climbs. I'm not sure how 673 ft compares to other courses, but this is a tough run course, especially the last 5 miles.

The last 2 years have been hot there, especially 2016. But the 2 years before that the weather was fairly mild. For the 70.3 WC last year on Sept 10, we also had nice weather (and it was even wetsuit legal). I don't think the humidity there is horrible, but I live in the south. I think it's just a tough run, following a bike with 4 extra miles.