Sydney, one of Australia's most vibrant cities, boasts a climate that is as diverse as its culture and landscape. Classified as having a humid subtropical climate under the Köppen–Geiger system, Sydney experiences "warm, sometimes hot" summers and "generally mild" to "cool" winters. However, the city's weather is not without its extremes, influenced by phenomena such as the El Niño–Southern Oscillation, the Indian Ocean Dipole, and the Southern Annular Mode.

Located on the coast, Sydney's weather is moderated by its proximity to the ocean, though inland areas often experience more extreme temperatures. The city's primary weather station at Observatory Hill has recorded extreme temperatures ranging from scorching highs of 45.8 °C (114.4 °F) to chilly lows of 2.1 °C (35.8 °F). Days with temperatures at or above 30 °C (86 °F) are common, particularly in the central business district, while the metropolitan area may experience between 35 and 65 such days annually, depending on the suburb.

Sydney's climate exhibits an urban heat island effect, with certain parts of the city, especially coastal suburbs, more vulnerable to extreme heat. Summers can see temperatures exceeding 35 °C (95 °F), often alleviated by southerly buster winds bringing relief. Dry, westerly foehn winds occasionally occur in winter and early spring, contributing to warm maximum temperatures.

Rainfall in Sydney has historically been fairly uniform throughout the year, but recent years have seen a shift towards more summer-dominant and erratic patterns. Late summer through early winter typically sees higher precipitation, with east coast lows and nor'easters bringing heavy rain events. Snowfall is a rarity, last reported in 1836, though occasional graupel showers have been mistaken for snow. In 2009, the city experienced a severe dust storm amid dry conditions.

Exploring Sydney's climate reveals a dynamic interplay of factors, from seasonal variations to the influence of global oscillations, shaping the city's weather patterns and contributing to its unique atmospheric character.