I have booked to visit Taipei on 12/9 - 22/9 so how will the weather be at that times?

Hi, it will be hot and a little wet then, with the lowest temperature of 21-22C and the highest temperature of abnout 31C. Therefore, summer clothes are needed as well as a light coat to keep warm at cool nights or rainy days. As it would be still during the typhoon season, you'd better pay attention to the weather forecast before traveling in case your trip being spoiled.