I can’t really run because of my arthritis so running is out of the question. It needs to be something that is low impact on my joints but can help me loose weight. I want to loose 30 pounds before the beginning of high school on september 7th. Thanks for the help!

Thirty pounds is a lot of weight to lose in a little over a month.
If you have access to a pool, swimming is the one of the best options for those suffering from arthritis. It is easy on the joints and it is a good workout.
Walking is also a low-impact exercise. Yoga and Tai Chi seem very helpful for arthritis sufferers as well.
Good Luck!