Australia is only slightly smaller than the United States, but in its sparse population, it can be compared with Canada. Much of Australia is warm or hot around the year and even along the cooler southern coasts the winters are mild rather than cold. Only Tasmania has a temperate climate comparable to that of Britain. Very high temperatures occasionally occur almost anywhere in Australia when winds blow out from the interior and import the high temperatures and low humidities of the interior desert to the coastal regions. Only Tasmania escapes these extremes of heat, and also has abundant rain all year round. Serious bush fires can be caused by the prolonged heat waves and drought. The country can essentially be split into four climatic regions: the tropical region of the north and north-east, south-eastern Australia, southern and western Australia, and the desert and semi-arid regions of central Australia. To these can be added the temperate climate of Tasmania.
The tropical region of the north and north-east consists of the coasts of Queensland, the Northern Territory and Western Australia and the inland districts which have more than 500 mm (20") annual rainfall. At Brisbane, winter temperatures are close to those normally regarded as having a tropical climate. The daily average maximum temperatures range from 29 °C (85 °F) in summer to 20 °C (68 °F) in winter. It differs from places farther north in that it gets rain in all months, whereas Townsville and Cairns are more typically tropical in having a virtual drought during the low sun months. In the high sun period, the weather can be very sultry and oppressive, but the higher temperatures and lower humidities experienced inland towards the dry interior are more bearable than the coastal sticky heat. Like most of Australia, this region has a very sunny climate with daily sunshine hours averaging 6-7 hours during the wetter cloudier months and 8-10 hours during the dry months. Tropical cyclones occur two or three times a year in the seas to the northeast and northwest of Australia. The northern part of the Queensland coast and the coast from Darwin southwards are affected by the torrential rain and sometimes very high winds near the storm centres.
South-eastern Australia comprises Victoria and the greater part of New South Wales (excluding the drier western and northwestern region of that state). It has a climate that can best be described as warm-temperate with no real cold season, warm to hot summers and a good distribution of rainfall throughout the year. The weather can be changeable throughout the year and the summers are liable to prolonged heat waves and droughts. Cold spells are brief and never severe on the coast. For example the lowest average daily monthly temperatures are 13 °C (56 °F) at Melbourne and 16 °C (61 °F) at Sydney. Inland (e.g. Canberra), much lower temperatures are possible, indeed a low of -10 °C (14 °F) has been recorded. Both Melbourne and Sydney occasionally record temperatures of 38 °C (100 °F), whilst the number of sunshine hours is affected by the latitude. Summer sunshine averages 8-9 hours, but the winter value is only 5-6 hours.
Southern and western Australia consists of two small districts separated by the desert coast along the Great Australian Bight where the annual average rainfall is below 250 mm (10"). The area around Spencer Gulf in South Australia, parts of western Victoria and the south-western part of Western Australia are distinctive in having a Mediterranean type of climate. Rainfall is moderate and falls mainly in the winter. Summers are warm to hot with an almost complete drought, whilst the winter gets very changeable weather associated with cyclonic disturbances. Perth and Adelaide represent the wetter parts of the two districts, and the mildness of the winter is mirrored by the fact that an air frost has never been recorded at either location. The winter maximum of rainfall is clearly marked at both places, but Perth has a much higher annual rainfall (881 mm) than Adelaide (535 mm). During the hot dry summer, temperatures can rise to over 43 °C (110 °F).
The desert and semi-arid region is the most extensive climatic region of Australia, including part of every mainland state except Victoria. Rainfall everywhere is scanty and unreliable, and the cool season rainfall of the south is much more effective than the hot season rainfall of the tropical north. Like most continental interiors there is a considerable daily and seasonal change of temperature. Places in the centre of the region, such as Alice Springs, have experienced regular air frosts. These desert areas are the sunniest part of Australia, enjoying nearly ten hours per day all year round. The high temperatures (often well in excess of 40 °C - 104 °F) are sometimes compensated by low humidities, and occasional duststorms are to be watched for. Tasmania is a small rugged mountainous island with large variations in weather and climate. The mountains rise to 5,000 ft and are exposed, on the west, to the stormy westerly winds which bring heavy rain (2,500 mm - 100" per year) in places.
Tasmania's climate is strongly influenced by the relative warmth of the southern ocean so that winters are mild at sea level and summers rarely too hot. The occasional high temperatures (38 °C - 100 °F) occur when very warm air is drawn southwards from the central region. Although snow is often heavy in winter on the mountains it does not lie throughout the summer.