I really like using worldweather.org
Aside from weekly forecasts they list temperature averages, both minimum and maximum for each month as well as average number of rain days and total amount of rain per month.
You can find the entry for Hong Kong here http://www.worldweather.org/002/c00001.htm
If you are cruising HK to Sing you will pass Malaysia. Here is the link for Penang and Melaka (Malacca) in Malaysia
Link for Singapore