Will leaves turn yellow and red in 16 September to 24 september at Jiuzhaigou?

Yes, they will and it is during the best timing to see the leaves.

According to the weather records in the past years, it would be a little cool, with the temperature range of 14℃ to 23℃. You can wear long-sleeved shirt, jacket and regular jeans. There would be some cloudy days, but rainy days would also happen, so prepare rainy gear.