how about the Hong Kong weather between June 19 to June 30, 2014

Hi, now it is hard to tell the exact weather during your visiting, but only a general information can be told based on the previous records.
The average temperature is around 25 to 30C, hot and a little bit humid. So the summer clothes are enough. Besides, I suggest you to prepare a thin coat and use it when you are shopping in the malls.
Hope it helps ~