Sydney’s climate is classified as humid subtropical (Cfa) under the Köppen–Geiger classification system, which leads to warm, often hot summers and mild to cool winters. The city’s weather is significantly influenced by the El Niño–Southern Oscillation, the Indian Ocean Dipole, and the Southern Annular Mode. These climatic factors contribute to a range of weather patterns, from drought and bushfire conditions to storms and flooding, depending on the phase of these oscillations.

The proximity of Sydney to the ocean plays a moderating role in its weather, although more extreme temperatures can be recorded in the inland western suburbs. For instance, Sydney's primary weather station at Observatory Hill has documented extreme temperatures, reaching up to 45.8 °C (114.4 °F) on January 18, 2013, and dropping to 2.1 °C (35.8 °F) on June 22, 1932. The central business district (CBD) typically experiences an average of 14.9 days each year with temperatures at or above 30 °C (86 °F), while certain suburbs may see this figure rise to between 35 and 65 days annually. The highest temperature recorded in the metropolitan area was 48.9 °C (120.0 °F) in Penrith on January 4, 2020.

Sydney enjoys a significant amount of sunshine, averaging 7.2 hours per day and recording 109.5 clear days annually. Due to its inland location, frost can occasionally occur in Western Sydney during winter. The transitional seasons of autumn and spring show considerable temperature variations, with spring typically experiencing more significant fluctuations.

The city is also affected by the urban heat island effect, which leads to higher temperatures in certain areas, particularly coastal suburbs. During late spring and summer, temperatures exceeding 35 °C (95 °F) are common. However, these hot, dry spells are often interrupted by a southerly buster, a powerful southerly wind that can bring gale-force winds and a swift drop in temperature. Additionally, Sydney occasionally experiences dry, westerly foehn winds during winter and early spring, which contribute to the higher maximum temperatures in the region. When the Roaring Forties shift towards southeastern Australia, these winds can become intense, potentially causing damage and affecting air travel.

Rainfall in Sydney has moderate to low variability, with historical patterns indicating relatively uniform precipitation throughout the year. However, recent trends have shown a tendency toward summer-dominant and erratic rainfall. Typically, higher precipitation occurs during the summer and autumn months, while late winter and early spring tend to see less rainfall. Notably, east coast lows can deliver significant rain in the CBD during late autumn and winter, while summer brings heavy rain events often associated with black nor’easters or remnants of ex-cyclones.

Although snowfall is extremely rare in Sydney, the last recorded instance occurred in 1836. In July 2008, graupel, or soft hail, was mistaken for snow in the Upper North Shore. The city also faced a severe dust storm in 2009 due to dry conditions, illustrating the diverse and sometimes extreme weather patterns that characterize Sydney’s climate.

In summary, Sydney's climate is marked by its humid subtropical nature, seasonal temperature fluctuations, and diverse weather patterns influenced by various oceanic and atmospheric phenomena, making it a unique environment for both residents and visitors.