Keep in mind that Australia is a continent as well as a country and that the climate varies accordingly. The variations are not as great as in America, but sharp enough to make you regret wearing the wrong clothes during certain seasons. The seasons are the reverse of those in the northern hemisphere: September to November is spring, December to February summer, March to May fall, and June to August winter.

The climate regions are upside down as well. The tropics lie north, the temperate zones south. Tasmania, the island state off the southern tip of the continent, is the coolest, while north of Brisbane things get pretty hot most of the year. As a general rule you can assume that from November to March it's warm everywhere. In the far north, around Darwin, is the monsoon season and definitely a time to stay away unless you enjoy getting drenched in rainwater. But the northern winter offers close toideal traveling weather. In the south, winter tends to be chilly, with plenty of snow.
All a around Australia has superb tourist weather, particularly in the capital cities which lie outside the extreme hot and cold belts.