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Sydney’s climate, classified as humid subtropical (Cfa) under the Köppen–Geiger system, is characterized by hot, often sweltering summers and mild to cool winters. The city's weather patterns are shaped by significant climatic forces, including the El Niño–Southern Oscillation, the Indian Ocean Dipole, and the Southern Annular Mode. These drivers contribute to both extreme drought and bushfire conditions, as well as storms and flooding, depending on the phase of the oscillation. Proximity to the ocean helps moderate Sydney’s climate, with coastal areas generally experiencing milder conditions than the more inland western suburbs.
At Sydney’s Observatory Hill, temperature extremes have ranged from a scorching 45.8°C (114.4°F) on January 18, 2013, to a chilly 2.1°C (35.8°F) on June 22, 1932. The city’s central business district typically experiences 14.9 days a year with temperatures exceeding 30°C (86°F), while the western suburbs see between 35 to 65 such days annually. The highest temperature recorded in the metropolitan area occurred in Penrith on January 4, 2020, when the mercury hit a blistering 48.9°C (120.0°F).
Sydney’s coastal waters maintain an average sea temperature ranging from 18.5°C (65.3°F) in September to 23.7°C (74.7°F) in February. The city enjoys an average of 7.2 hours of sunshine per day, with 109.5 clear days each year. However, frost can occur in the mornings in Western Sydney during winter. Spring and autumn are transitional seasons, with spring showing greater temperature variations than autumn.
The city also grapples with the urban heat island effect, where urban areas experience higher temperatures than surrounding rural areas, making certain parts of Sydney particularly vulnerable to extreme heat. Late spring and summer often see temperatures surpassing 35°C (95°F), though these conditions are usually relieved by a southerly buster—a gusty southerly wind that rapidly drops temperatures and can bring heavy winds. Additionally, Sydney occasionally experiences dry westerly winds during winter and early spring, known as foehn winds, which can intensify temperatures and cause significant damage to homes and infrastructure.
Rainfall in Sydney is moderate, with variability decreasing over recent years, as the city has seen more erratic and summer-dominant precipitation patterns. Heavy rainfall often occurs during summer through autumn, while late winter and early spring are typically drier. East coast lows in late autumn and winter can lead to significant rainfall, particularly in the CBD. In summer, black nor’easters are often responsible for heavy rains, and remnants of ex-cyclones or low-pressure systems can bring further deluge. Although rare, snow-like phenomena, such as graupel, have been reported, with one instance in 2008 where a fall of graupel was mistakenly believed to be snow. Dry conditions, such as those in 2009, can also lead to severe dust storms.
Sydney's climate is an ever-changing balance of extreme temperatures, seasonal shifts, and unpredictable weather patterns, all influenced by the interplay of global climate forces.