Sydney enjoys a mild climate year-round, with over 340 sunny days a year. Remember that seasons in the Southern Hemisphere are reversed -- January is midsummer and July is midwinter.
Spring (September to November) is arguably the best time to visit. Temperatures range from 19 to 25 degrees, the jacarandas bloom purple across the city, and the beaches are uncrowded. Vivid Sydney, the city's major light and music festival, runs in late spring.
Summer (December to February) brings warm days of 25 to 30 degrees, spectacular New Year's Eve fireworks over the harbour, and packed beaches. It is also the wettest season, with occasional heavy afternoon storms.
Autumn (March to May) offers comfortable temperatures from 17 to 25 degrees and fewer tourists. The Royal Easter Show in April is a beloved local tradition.
Winter (June to August) is mild by world standards, with highs of 16 to 18 degrees and lows rarely dropping below 8. You will not need more than a light jacket most days. The Sydney Film Festival runs in June.