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This FACT indicates the average annual morning relative humidity measured at 9am in each Australian city between the years 1981 and 2010. The relative humidity measures the amount of water vapour in the air as a percentage of the maximum water vapour the air can hold. Therefore relative humidity is measured as a percentage. A relative humidity reading of 100% means that the air is completely saturated with water and cannot hold anymore. Relative humidity near the ground could be much less, therefore there does not need to be a reading of 100% for it to be raining. Rather surprisingly, the city with the highest average humidity is Canberra, at 73 percent. The city with the lowest is tied between Adelaide and Perth, at 62 percent.