Northern lights in late August

I am a not so seasoned traveller coming to iceland for the first time for a 5 day solo trip. I have opted to travel through tours. I am really excited to do a northern light guided tour but I am trying to set realistic expectations as I know that it is only the beginning of the season for late august and it might be too cloudy. I was wondering if I should book the tour now or should I wait to book it until the last minute as to check the whether forcast around that time? Would love to hear if there is anyone who succeeded in seeing them in late August (I planned to book the tour on the 24th).