In terms of climate winter does not necessarily mean the air is more humid. And summers do not necessarily mean that the air is more humid. It varies by location. Melbourne tends to be more humid in the colder months, drier in summer.
View attachment 248827
Whereas Sydney is the opposite.
View attachment 248828
Relative humidity is the amount of moisture in the air relative to the amount of moisture the air can hold. Warm air can hold a lot more moisture than cold air. Given the above figures, both Sydney and Melbourne have higher absolute humidity in summer than in winter.