Climate of Perth Airport

Perth experiences a Mediterranean climate, characterised by hot, dry summers and mild, wet winters. These seasons extend into the autumn and spring months, which are transitional periods between the main seasons.

The climate of the region is strongly influenced by the position of the axis of the band of high pressure known as the sub-tropical ridge, and in the warmer months by the development in the easterlies to the north of the ridge of a trough of low pressure near the West Coast. For much of the year the ridge is located to the south allowing the east or southeasterly winds to prevail. During the cooler months the ridge periodically moves to the north allowing cold fronts to pass over the west coast and deliver much of the annual rainfall. Sometimes these fronts interact with tropical cloud bands from the northwest and this can enhance the amount of rainfall produced.

Of the annual mean rainfall of 869 mm, which occurs on 119 rain days, about 80% usually falls between May and September. Rain occurs on four days out of every seven on average during winter. Flooding is rare in Perth, however heavy rain may be produced by strong winter cold fronts or, less frequently, by summer storms or, more rarely, by decaying tropical cyclones. The highest daily rainfall is 120.6 mm recorded on 9 February 1992.

In contrast to winter rainfall, the mean summer rainfall is just 36 mm on an average of 10 rain days. It is not unusual for there to be extended dry periods during the warmer months. Perth had 83 days without rain between 15 December 1974 and 7 March 1975. In the six months from November 1993 to April 1994 a meagre 19.2 mm of rain fell.

Mean monthly air temperature range from 31°C in February to 18°C in July and August. Summer maximum temperatures are strongly dependent upon the arrival time of the reliable sea breezes. On some days the difference between the maximum temperatures on the coast and the eastern suburbs may exceed 10°C. Heatwaves are associated with strong easterly winds and the late arrival or absence of the sea breeze. In February 1975 and 1988 there were ten consecutive days when the temperature exceeded 35°C. The highest temperature ever recorded is 46.2°C, however, the temperature exceeds 40°C on only three days per year on average.

The average minimum temperature ranges from just 8°C in July and August to 17°C in January and February. Temperatures below 5°C are not uncommon during any of the winter months. The lowest temperature ever recorded at Perth Airport is –1.1.

Winds are mainly easterly but varied in the warmer months by reliable afternoon sea breezes and in the cooler months by the westerlies that are associated with the bulk of the annual rainfall. Despite the occurrence of strong winds or gales, average wind speeds in winter are considerably lighter than in summer.

Mean daily pan evaporation ranges from a maximum of about 10 mm in January to just 2 mm in June and July. The average annual evaporation exceeds 2000 mm.

Perth is one of the sunniest Australian cities and enjoys an annual average of over 8 hours of sunshine per day. In the predominantly clear days of summer the average daily sunshine duration exceeds 11 hours.