The heat can be your friend if you are looking to lose a few pounds. It is certainly not hard to work up a sweat when it is 90% outside and you are jogging up a hill. You do have to make sure that you are being safe about it though. You have to have water with you, and you have to to take frequent heat stress breaks. Following some simple safety rules can go along way. Once you are confident that you have everything in line, you should be good. This is when cardio and heart rate will work big time.
Get out side with your dumbells, and do some circuit workouts with them. You will kill 2 birds with one stone like this. You can build muscles and lose fat at the same time. What ever you do make sure that you are not going overboard. Over doing it in the heat is not a good idea. Some gyms offer an outside, beach like environment that you can use. This is a really good way to get a tan and workout all at once. These are some really good cardio workouts.
This is not for everyone, but if you are up to it you should give it a try. Start out by doing these workouts maybe once or twice a week and see how it makes you feel. It is a great way to lose weight, because you burn a ton of calories, and sweat alot. Both of these things are key to losing weight. You just have to really want to do it I guess.