Typhoons are like hurricanes. So there is really no way to predict if the Typhoon warning will go higher than 8. I thnk planes can still TAKE OFF from HKG at typhoon warning 6 or 7.

I was on a flight once from YVR where the prediction was that the typhoon will pass or be washed out. But about two hours out of HKG, I noticed the plane slowly changing course and descending. Soon we were advised that due to Typhoon, the flight would land in TPE instead. CX took care of all transfers, and arrangements and we flew off for HKG the next day.

So really, no one knows. Not even weather predictions.