Summer in Australia is generally a season of fun, sun and festive times. It begins on December 1 and continues until the end of February.
For those visiting Australia from northern hemisphere countries such as the United States, Canada, England and the northern countries of Asia and Europe, the Australian summer almost exactly coincides with the northern winter.
So northern travelers should keep in mind that they are journeying from winter to summer and should accordingly dress for the season in their country of arrival.
source – About Travel