Perth receives moderate, though highly seasonal, winter based rainfall. Summers are generally hot, sunny and dry, lasting from December to March, with February generally the hottest month. Winters are relatively cool and wet, giving Perth a hot-summer Mediterranean climate . Perth has an average of 8.8 hours of sunshine per day, which equates to around 3,200 hours of sunshine and 138.7 clear days annually, making it Australia’s sunniest capital city.
Summers are dry but not completely devoid of rain, with sporadic rainfall in the form of short-lived thunderstorms, weak cold fronts and on occasions decaying tropical cyclones from Western Australia’s northwest, which can bring heavy rain. Temperatures above 40 °C (104 °F) are fairly common in the summer months. The highest temperature recorded in Perth was 46.2 °C (115.2 °F) on 23 February 1991, although Perth Airport recorded 46.7 °C (116.1 °F) on the same day. On most summer afternoons a sea breeze, known locally as the “Fremantle Doctor”, blows from the southwest, providing relief from the hot northeasterly winds. Temperatures often fall below 30 °C (86 °F) a few hours after the arrival of the wind change. In the summer, the 3 p.m. dewpoint averages at around 12 °C (54 °F).
Winters are cool and wet, with most of Perth’s annual rainfall between May and September. Winters see significant rainfall as frontal systems move across the region, interspersed with clear and sunny days where minimum temperatures tend to drop below 5 °C (41 °F). The lowest temperature recorded in Perth was −0.7 °C (30.7 °F) on 17 June 2006. The lowest temperature within the Perth metropolitan area was −3.4 °C (25.9 °F) on the same day at Jandakot Airport, although temperatures at or below zero are rare occurrences. The lowest maximum temperature recorded in Perth is 8.8 °C (47.8 °F) on 26 June 1956. It occasionally gets cold enough for frost to form. While snow has never been recorded in the Perth CBD, light snowfalls have been reported in outer suburbs of Perth in the Perth Hills around Kalamunda, Roleystone and Mundaring. The most recent snowfall was in 1968.
The rainfall pattern has changed in Perth and southwest Western Australia since the mid-1970s. A significant reduction in winter rainfall has been observed with a greater number of extreme rainfall events in the summer, such as the slow-moving storms on 8 February 1992 that brought 120.6 millimetres (4.75 in) of rain, heavy rainfall associated with a tropical low on 10 February 2017, which brought 114.4 millimetres (4.50 in) of rain, and the remnants of ex-Tropical Cyclone Joyce on 15 January 2018 with 96.2 millimetres (3.79 in). Perth was also hit by a severe thunderstorm on 22 March 2010, which brought 40.2 mm (1.58 in) of rain and large hail and caused significant damage in the metropolitan area.
The average sea temperature ranges from 18.9 °C (66.0 °F) in October to 23.4 °C (74.1 °F) in March.