I'm planning to go taiwan in May next year. How's the weather from during mid may?

May is the plum rain season and it always rain.
The average temperature is around 18 to 28C, but it is different between the north part and the south part.
In south part, it may not rain a lot and the short sleeved clothes are enough.
In north part, the short sleeved clothes and a thin coat are necessary. Rain gear are needed.