Cyclones: Get the facts

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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
1.2 – 1.6m Slight damage
Trees and farmland damaged.
2 126 – 169km/hr
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 cycloneThe eye of a swirling cyclone
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?

  1. The average life of a cyclone is 1 week.
  2. After the eye passes, and the other side of the cyclone hits, the wind blows with equal strength but in the opposite direction.
  3. Tropical Cyclones, from the Southern Hemisphere spin clockwise, and Hurricanes and Typhoons in the Northern Hemisphere spin anti-clockwise.
  4. Cyclone Tracy was Australia’s most destructive cyclone.
  5. 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?

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