The usual magic number is about 1 lb/week. But that will vary greatly depending on your method of weight loss and your exercise regiment.
I've heard you shouldn't lose more than 3 lbs/week for sustained loss. (Source? I don't remember if it was my doctor or not
Set yourself a moderate goal for now, like 1.5 lbs a week. If it's really easy, you can try pushing yourself to 2. But beyond that it's really hard. You need to either starve yourself (horrible idea, don't do it) or exercise a lot. But when you exercise a lot you need to eat more and that can feel counter-intuitive.
August may seem like forever but it's not!