Climate of Esperance

Esperance has a Mediterranean-type climate with warm, dry summers and cool, wet winters. It is subject to wide variations in the weather, from hot summer days when northerly winds arrive from the interior of the state, to cold, wet winter days with southerly winds from the Southern Ocean.

The climate is strongly influenced by the position of the band of high pressure known as the sub-tropical ridge. The seasonal variations are mainly due to the north-south movement of this ridge. Persistent east to southeast winds prevail in summer when the ridge is south of the state. The ridge moves north in the cooler months allowing the moisture-laden westerly winds south of the ridge to deliver much of the annual rainfall.

Cold fronts embedded in the westerlies are common in the winter months. Approximately 68% (418 mm) of the annual average rainfall (619 mm) occurs between May and October with July being the wettest month with an average of 99.7 mm. There can be considerable variation in the total rainfall from year to year. It has ranged from 1003 mm in 1968, to 404 mm in 1994. Other dry periods include 1896, 1914, 1919, 1954, 1969, 1977-78, 1982-83, 1991 and 1994.

January and February maximum temperatures average 26°C, although temperatures above 35°C occur about 11 times each year when dry north to northeasterly winds arrive from the interior of the state. The highest temperature recorded at the Meteorological Office was 46.7°C on 1 February 1991. Such high temperatures are usually followed by a dramatic cool change when the winds shift to the south and drop the temperature by up to 20°C. Occasionally the change is accompanied by a thunderstorm from the north or west that can produce a spectacular lightning display and strong winds. Winter daytime maximum temperatures average 17-18°C although it may be somewhat colder when strong southerly winds follow a cold front.

The ocean temperatures help to moderate overnight winter temperatures. July, the coldest month, has an average minimum temperature of 8°C and while the lowest minimum temperature recorded at the Post Office is -0.6°C. Temperatures below 4°C are rare.

Although fronts and depressions may bring strong to gale force winds, winter winds are more variable and generally lighter than those of summer.

Evaporation in the summer months is high with a January average of 240mm (8mm a day). The monthly evaporation decreases to 66mm in June (2mm a day). Daily evaporation can vary significantly from over 15mm on a hot windy summer day to almost negligible on a cold wet winter day.