I can personally vouch for the fact that when it gets hot, you are more uncomfortable when you weigh more. I think it has to do with the fat in your body acting as an insulator and not allowing your body's natural cooling system to work properly. It is times during heat waves that most people end up drinking more water and eating less. It is one of the quick weight loss programs that will work for a short period of time. Most of the weight lost will be water weight, but considering that the human body is made of 90% water then that is a lot of weight.
Stay cool and drink lots of water.