Cyclones and tornadoes are dangerous storms that can destroy things.
A tornado is a twisting wind storm.
A cyclone is a strong wind storm.
Hurricane is another name for a cyclone.
A tornado is a strong, twisting wind.
What is a cyclone?
Violent wind storms are called cyclones in Australia, and are known as typhoons or hurricanes in other countries.
A cyclone begins over warm tropical seas when a large mass of air rotates around an area of low atmospheric pressure. The warm, moist air becomes a strong, circling, wind storm.
Cyclones spiral clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere.
The eye of the storm
In the centre of a cyclone, there is a calm area called the 'eye'. In the eye, the sky is clear and there is only a light wind blowing.
Cyclones can change direction suddenly, which makes it very difficult for meteorologists to forecast what will happen.
Cyclones move at up to 360 kilometres per hour, bringing heavy rain and very high winds and causing high waves. The wind and rain cause lots of damage when the cyclone crosses over coastal lands.
The worst cyclone in Australia was Cyclone Tracy, which devastated the city of Darwin, Northern Territory on Christmas Eve 1974.
On December 20, 1974 the Bureau of Meteorology in Northern Australia noticed a cyclone forming off the coast. They named it Tracy.
The people at the weather bureau closely watched Tracy for the next few days but did not feel that the cyclone posed a major threat to Darwin. They thought that it would pass well to the north of Darwin.
However early on Christmas Eve, 24 December 1974, Tracy came closer, turned and began to speed towards the city. From midnight until 7am on Christmas Day the cyclone passed directly over Darwin. The wind speed was 217 kilometres per hour and Tracy brought huge rainfall. Houses and other buildings were blown apart, 49 people died in the city and another 16 were drowned at sea. Seven out of every ten of Darwin's homes were destroyed or severely damaged.
Communications, power, water and sewerage services were all broken. Emergency committees worked to provide accommodation, food and clothing to all those whose houses had been destroyed or damaged. Australia's defence forces took a major role in cleaning up the city and suburbs.
There was a threat of disease too because sewerage systems had been destroyed. In all, 25 000 people were evacuated to southern cities.
Between 1975 and 1976 over 150 million dollars was spent to build or repair more than 2 500 homes as well as other many other buildings.
Hurricanes (cyclones) in Action (watch the video)
What is a tornado?
A tornado is a violent, twisting windstorm. A tornado forms when air in a thunder cloud is set spinning by wind, and more and more air is sucked up into a spinning column like a giant vacuum cleaner.
Tornadoes cause great damage. They suck up dust, uproot trees, overturn cars and buildings, and lift roofs and even people.
Tornadoes in deserts are sometimes called 'dust devils', and in Australia, an Aboriginal name for a tornado is 'willy-willy'.
How Does a Tornado Form?
The Beaufort Wind Scale
This is one way that the strength of the wind is measured. The scale is named after Sir Francis Beaufort, who developed it in 1805 for use by sailors. You can use the Beaufort scale to measure the force of the wind by looking at the effects of the wind on things around you.
Scale description: wind speed: You may see:
Force 0 calm 0 km per hour Smoke rises vertically
Force 1 light air 1-5 kph Smoke blown by wind
Force 2 light breeze 6-11 kph Leaves rustle, feel the wind on face
Force 3 gentle breeze 12-19 kph Moving leaves & twigs; flags flutter
Force 4 moderate breeze20-30 kph Wind raises dust and fallen leaves. Paper blows around. Small tree branches sway
Force 5 fresh breeze 31-39 kph Small trees begin to sway
Force 6 strong breeze 40-50 kph Large branches sway. Umbrellas hard to hold, blown inside out
Force 7 near gale 51-61 kph Whole trees sway. Feel the wind push you
Force 8 gale 62-74 kph Difficult to walk in the wind. Twigs broken off trees
Force 9 strong gale 75-87 kph Tiles blown off roofs, branches blown down
Force 10 storm 88-102 kph Houses damaged. Whole trees broken or blown over
Force 11 violent storm 102-116 kph Serious damage
Force 12 cyclone 117-132 kph Widespread damage