Is it safe to tour to Hongkong from 9-13 September, considering thunderstorms and typoon forecasts?

Generally speaking typhoon season is from late May to Mid October. If you choose to go in September, you may meet typhoon unluckily.
But please do not worry. You can pay attention on the weather forecast before your trip in order to see whether there is a typhoon or not. If you meet it unluckily, it is suggested stay in hotels or choose some nearby shopping malls to shopping.