Geography of Western Australia - The Climates of Western Australia

The Climates of Western Australia

Western Australia is divided in half climatically by a belt of descending dry high pressure system airflow, generally along the Tropic of Capricorn between the north, in which a summer rainfall pattern predominates, and the south, characterised by winter rainfall.

The northern part of the state, characterised by Monsoonal circulation, in the winter months from May to September is of generally warm dry offshore winds, drawn across the Inter-Tropical Convergence Zone by the low pressure systems of Monsoon Asia. In summer, from November to March, with the displacement of the Intertropical Convergence over northern Australia, the weather is characterised by humid tropical onshore airflows, coupled with thunderstorms and an occasional cyclone, these weather patterns bringing the bulk of the rainfall of the region. The highest wind-gust recorded on the Australian mainland was 259 km/h at Mardi during tropical cyclone Trixie, in 1975 and Whim Creek has the record for the highest rainfall, at 747 mm in 24 hours, associated with a cyclone in 1898.

In the southern part of the state the bulk of rainfall comes from west to east moving cold frontal low pressure depressions, originating off the edge of the winter pack-ice in the Southern Ocean, south of South Africa. Cold southern airflows, wedging beneath humid north westerly winds triggers vertical instabilities, bringing this region the bulk of its rain between May and August. During the summer months these frontal depressions travel well to the south, leading to warm high pressure systems dominating the southern part of the state.

As a result the state is classified with five climates in the Köppen climate classifications, ranging from Aw Tropical wet-dry climates in the Kimberley region of the state, through BSh Semiarid (summer rainfall) to the south of the Kimberley, BW Arid climates, covering the Great Sandy Desert, Central Australian Desert, Gibson Desert and the Great Victoria Desert, BSh Semiarid (winter rainfall), from Shark Bay to the Nullabor, and then a Csa Mediterranean climate from Northampton to Esperance and covering the Southwest of the state.