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Cyclones – Get the Facts
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.
In order for it to be categorised as a cyclone, its average sustained wind speed needs to exceed 63 kilometres per hour. To be classified as severe, the average sustained wind speed needs to exceed 118 kilometres per hour.
Once they arrive over land, their strength weakens and they begin 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.
Severity and Categories
Cyclones are categorised according to their strength. There are 5 categories: Category 1 is the weakest and Category 5 is the strongest.
| Category | Wind Gusts | Ocean Swells | Damage |
|---|---|---|---|
| 1 | Up to 125km/hr Gales |
1.2 – 1.6m | Slight damage Trees and farmland damaged. |
| 2 | 126 – 169km/hr Destructive |
1.7 – 2.5m | Significant Damage Minor house damage. Severe damage to signs and trees. Heavy damage to crops |
| 3 | 170 – 224km/hr Very Destructive |
2.6 – 3.7m | Structural damage House roofs and most likely power failures |
| 4 | 225 – 279km/hr Very Destructive |
3.8 – 5.4m | Significant roofing and structural damage Airborne debris, widespread power failure |
| 5 | Winds above 280km/hr Very Destructive |
More than 5.5m | Almost total destruction and extremely dangerous Houses flattened, cars over turned |
Every cyclone has an ‘eye’
The eye of a swirling cyclone.
The eye is in the centre of the cyclone and can vary in size, from 10 kilometres to 100 kilometres, depending on the severity of the storm.
Do not be fooled by the eye!
Due to the least amount of air pressure in the eye, it produces clear weather with light wind, no clouds, no rain and some sunshine. But, the storm is not over yet.
This is only the middle of the storm. Depending on the wind gusts, the eye may pass in a few minutes or in a few hours.
You are always advised to stay indoors during the passing of the eye of the storm, because the cyclone will continue. Always listen for the official word that the cyclone has passed and when it is safe to leave your shelter.
When going outside, be aware of fallen powerlines, debris and damage left behind after the cyclone.
Did you know?
- The average life of a cyclone is 1 week.
- After the eye passes, and the other side of the cyclone hits, the wind blows with equal strength but in the opposite direction.
- Tropical Cyclones, from the Southern Hemisphere spin clockwise, and Hurricanes and Typhoons in the Northern Hemisphere spin anti-clockwise.
- Cyclone Tracy was Australia’s most destructive cyclone.
- Cyclones are assigned names, which are picked from a list.
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.
Australian Region Names
| A | Anika | Anthony | Alessia | Alfred | Ann |
|---|---|---|---|---|---|
| B | Billy | Bianca | Bruce | Blanche | Blake |
| C | Charlotte | Carlos | Cathy* | Caleb | Claudia |
| D | Dominic | Dianne | Dylan | Debbie | Damien |
| E | Ellie | Errol | Edna | Ernie | Esther |
| F | Freddy | Fina | Fletcher | Frances | Ferdinand |
| G | Gabrielle | Grant | Gillian | Greg | Gretel |
| H | Hamish* | Heidi | Hadi | Hilda | Harold |
| I | Ilsa | Iggy | Ita | Ira | Imogen |
| J | Jasper | Jasmine | Jack | Joyce | Joshua |
| K | Kirrily | Koji | Kate | Kelvin | Kimi |
| L | Laurence | Lua | Lam | Linda | Lucas |
| M | Magda | Mitchell | Marcia | Marcus | Marian |
| N | Neville | Narelle | Nathan | Nora | Noah |
| O | Olga | Oswald | Olwyn | Owen | Odette |
| PQ | Paul | Peta | Quang | Penny | Paddy |
| R | Robyn | Rusty | Raquel | Riley | Ruby |
| S | Sean | Sandra | Stan | Savannah | Seth |
| T | Tasha | Tim | Tatjana | Trevor | Tiffany |
| UV | Vince | Victoria | Uriah | Veronica | Verdun |
| WXYZ | Zelia | Zane | Yvette | Wallace |
* Cyclone names marked for replacement.
Could a cyclone be named after you?
Is your name on the list?