What are cyclones? • Cyclones are giant, spinning whirlwind storms. In order for a cyclone to be identified as a cyclone, it must be travelling over 119 kilometres per hour and it must have been formed over the ocean in a tropical region. • In North America, they are called hurricanes and are called typhoons in Asia. • Tropical cyclones, in the Southern Hemisphere spin clockwise, and hurricanes and typhoons in the Northern Hemisphere spin anti-clockwise. The average life of a cyclone is one week.
How are cyclones formed? • Tropical cyclones are formed over the ocean in the area around the equator, between the Tropic of Cancer and the Tropic of Capricorn. In order for a cyclone to form, the ocean waters need to be warm, at least 26°C. • Above the warm ocean, water evaporates and form clouds. If there is low air pressure where the clouds are formed, it pulls them in and they begin to rotate. It is the Earth’s rotation and spinning on its axis that causes the cyclone’s clouds to rotate. Clouds will continue to form and begin spinning more. • This is the stage when it can develop into a mature cyclone, or lose its momentum. Even if it has developed into a mature cyclone, it can still grow in size and increase its wind speed. • Once a cyclone arrives over land, its strength weakens and it begins to fade out. This is due to the lack of moisture and heat compared to the ocean over which it was formed.
How often do they occur? • Cyclone season in Australia is between November and April, but cyclones can still occur in the month of May. • The season for hurricanes and typhoons in the Northern Hemisphere is between June and November. • According to the Bureau of Meteorology, Australia has on average 13 cyclones a year. Half of these occur in the western regions.
The Eye of a Cyclone • The eye is in the centre of a cyclone and can vary in size, from 10 kilometres to 100 kilometres, depending on the severity of the storm. • Due to the least amount of air pressure in the eye, it produces clear weather with light winds, no clouds, no rain and some sunshine. • After the eye passes, and the other side of the cyclone hits, the wind blows with equal strength but in the opposite direction.
Names of Cyclones • Each cyclone is named from one of the names in the below table. The names start from the top of the list and take it in turns to be a male or female name. Once the end of the list is reached it begins again.
Areas Prone to Cyclones • The most cyclone prone areas include Queensland, Western Australia and the Northern Territory.
Cyclone Tracy, Dec1974Northern Territory • Tropical cyclone Tracy struck Darwin in the early hours of Christmas Day, 1974 and was rated a Category 4. Before the failure of instruments, the wind gauges registered speeds of 217km per hour. Cyclone Tracy caused massive and infrastructure damage as well as huge commercial and industrial losses. Over 80 percent of all buildings were destroyed or seriously damaged. The cyclone resulted in the death of 71 people, which included 22 who were lost at sea. Approximately 35,000 people in a population of 47,000 were evacuated due to the lack of food, shelter, water, medical aid and the threats of the spread of diseases.
Cyclone Yasi, Jan 2011Queensland • Cyclone Yasi developed as a tropical low north-west of Fiji 29 January, 2011. On 30 January it was named Yasi by the Fiji Meteorological Service. On 2 February it was upgraded a Category 5 system and made landfall near Mission Beach early on 3 February. • Significant wind damage was reported between Innisfail and Townsville. The towns of Tully and Cardwell suffered major damage to structures and vegetation. There was one recorded death. The largest rainfall totals of 200 – 300mm in 24 hours between Cairns and Ayr, causing some flooding. A 5 metre tidal surge was observed at Cardwell.