I completed W9R3 yesterday evening. Up until W8R2 I had been doing all runs outside, but W8R1 nigh on killed me (heat & humidity) so I did the rest of W8 and first 2 of W9 on the treadmill. However, I was determined to do the final run outside again.
I took it VERY slow, and survived! Mind you Garmin says it was "30ºC, 75% humidity, feels like 36.1ºC". Felt better than at the end of W8R1. I'll keep going and hope that as my fitness improves further I can better acclimatize to running in this heat too.