hi! will be in hk his oct 4-7 2017, what's the weather in those days? do they have sales?

According to forecast, the temperature may range from 25C to 30 C, and there may be some cloudy & rainy days. You are suggested to take you t-shirts, shirts, jeans, and light coat.
As for the sales promotion, generally speaking, lots of shops will have sales for 20-30 percent off during the golden week.