Yea honestly im sorry to say but losing 80lbs until December 1 is going to be super unhealthy for you thats gonna have to be an almost 6000 calorie deficit per day which means basically no food and alot of exercise. Even if ypu starve yourself all the way to december you sadly wont hit your goals. Though I would say since you are by definition obese you might wanna go to your doctor to get setup with a healthy plan. Im sorry to say but anything over 2-3lbs a week is going tp be super unhealthy for you and to hit your goal you are looking at a loss of 9lbs per week. I wish you look and dont let the numbers stop you. you WILL get there but just not that fast.