What are facts about cyclones?

Answer 1

1. The average life of a cyclone is 1 week, but they can last several weeks whilst out at sea.
2. Cyclones need sea temperatures of 26.5 degrees Celsius or higher to form.
3. Once cyclones make landfall, they usually last just a matter of hours before degenerating into tropical depressions, which often bring huge amounts of rain.
4. After the eye passes, and the other side of the cyclone hits, the wind blows with equal strength but in the opposite direction.
5. The winds of tropical cyclones, from the Southern Hemisphere, rotate clockwise, and hurricanes and typhoons in the Northern Hemisphere spin anti-clockwise.
6. Cyclone Tracy was Australia's most destructive cyclone in termsof damage to houses and buildings.
7. Cyclone Mahina, which hit north Queensland on 4 March 1899, was a category 5 cyclone, and resulted in the greatest death toll of any natural disaster in Australia.
8. Cyclones are assigned names, which are picked from a list.
9. Cyclone season in Australia is between November and April, although cyclones have been known to occur in May; in the northern hemisphere, hurricane/typhoon season is between June and November.
10. Cyclone intensity is measured by wind speed, and cyclones are accorded a category based on the following:

• Category 1 - gales with gusts to 125 km/h
• Category 2 - destructive winds with gusts of 125 -170 km/h
• Category 3 - very destructive winds with gusts of 170 - 225 km/h
• Category 4 - very destructive winds with gusts of 225 - 280 km/h
• Category 5 - very destructive winds with gusts exceeding 280 km/h

Answer 2

As warm, moist air over the ocean rises up from the ocean surface, there is less air left near the surface, and this causes an area of lower air pressure below. The air around this region has higher air pressure, and so it rushes in to fill the low pressure area. This air also becomes warm and moist and so it rises, too.

The cycle keeps going. Warm air rises, the surrounding air swirls in to take its place, and so on. When the warm moist air rises, it cools off, and the water in the air forms clouds. The whole system of clouds and wind spins and grows, because it is being constantly fed by the ocean's heat and water evaporating from the surface.

Some cyclones remain out at sea. Others come in to land, where they can cause considerable devastation. Once cyclones hit land, they dissipate. If they continue across a narrow section of land and hit water again, they sometimes re-form.

Answer 3

Australian cyclones most commonly occur off the northwestern coast of Western Australia, north of Darwin, the Gulf of Carpentaria and the Coral Sea. They occur in these areas primarily because the ocean sea temperatures are sufficiently warm enough to generate the right conditions. Further south, ocean currents do not get warm enough.

One of the worst cyclones to hit Australia was Cyclone Mahina, which hit Western Australia on 4 March 1899. It devastated hit a pearling fleet of around 100 vessels anchored at Bathurst Bay, pushing the boats onto the shore or into the sharp rocky reefs of the Great Barrier Reef. This killed 307 people; only 4 sailors survived. The final death toll of between 400 and 410 included at least 100 indigenous Australians, some of whom died when they were caught by the back surge and swept into the sea while trying to help shipwrecked men.

Another significant cyclone was Cyclone Tracy, which destroyed three-quarters of Darwin, the capital of the Northern Territory, on Christmas Day in 1974. Cyclone Tracy was a category 4 storm whilst still out at sea, but there is some evidence to suggest that it had reached category 5 status when it made landfall. The wind gauge at Darwin Airport officially recorded winds of 217 kilometres per hour before being blown away itself. Unofficial estimates suggest that the wind speed actually reached 300 kilometres per hour.