Newcastle enjoys a humid subtropical climate (Cfa), typical of Australia's east coast. Precipitation is most frequent during late autumn and early winter, while the second half of the year tends to be drier on average. The climate is moderated by the Pacific Ocean to the east, which helps temper the temperatures.

Summers in Newcastle are predominantly warm and humid, though there are occasional dry and hot spells due to hot west to north-western winds, which can push temperatures above 40 °C (104 °F). The highest recorded temperature was 42.5 °C (108.5 °F) on 18 January 2013 at the Nobbys Head weather station.

Winter in Newcastle is generally mild, with drier conditions compared to summer. While cold fronts can bring strong westerly winds, the region's location leeward of the Great Dividing Range results in clearer skies, thanks to the foehn effect. The lowest temperature ever recorded was 1.8 °C (35.2 °F) on 27 July 1986.

Newcastle is also affected by east coast lows, which can bring powerful winds exceeding 100 km/h (62 mph) and intense rainfall. These weather events usually last a couple of days and have occasionally caused significant disruption. Notable examples include the east coast low of May 1974, the 2007 New South Wales storms, and the April 2015 weather event. Despite these extremes, the overall climate remains mild and conducive to outdoor living throughout much of the year.