There are four seasons in Australia.

Summer is from December to February
Autumn is from March to May
Winter is from June to August
Spring is from September to November.

Rain is expected anytime through the year. Sometimes there are light showers and at other times thunder storms. In summer day temperatures can exceed 35 degrees Celsius and in winter the average day temperatures (June/ July) is 16 degrees Celsius.
For further information regarding climate in Australia please refer to: http://www.sydney.com.au/weather.htm