8 Mile Tempo Run

8 mile run, 6 miles as a pace run with 1 mile warm up and cool down. Ran in the afternoon, was above 80 and very humid. Was doing fine until about 2 miles in the pace part of the run, then I just got too warm, my heart rate was high, and I needed to slow down. Normally I would have taken only 1 water break during the pace part, but after the first 2 miles I needed to take one every mile. 8 miles in 1:17:22, average pace of 9:40, splits of 9:51, 8:55, 8:59, 9:19, 9:55, 9:55, 9:59 and 10:26. Average heart rate of 164, with the average of miles 2-6 of the pace part at 167 or 168. Going to need to start checking the weather to see if afternoon pace runs will be doable going forward.