I just had a surf onto the BOM Weather Radar Page for Sydney and it's been enhanced with some new features including weather observations available for the major weather locations/stations. If you run the cursor over the weather observations, you can get more detail such as the most recent humidity, temperature and dew point... could be handy!
For example, Blackheath at the moment shows the temp was 5°C with a dew point of 4.7°C at 6:00pm... so
if 
I was going out observing tonight, I'd be expecting dew very soon.
Al.