Hi, I just went to Dubai in early July. Very, very hot, around 40oC in day time and 33-35oC at night. But it's really fun and worth going. Certainly, it will be better to go in Christmas and New Year time but that was the peak season and everything is more expensive!
I found it's quite difficult to get much information from the Chinese or local website. To get more update information on Dubai trip you may visit the Dubai Forum in Tripadvisor