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What are they?

Tropical cyclones are formed over the ocean in the areas around the equator, between the Tropic of Cancer and the Tropic of Capricorn, and in order for a cyclone to form, the ocean waters need to be warm, at least 26C. Above the warm ocean, water will evaporate and form clouds (see our post on clouds) If there is a low pressure area where the clouds are formed, it pulls the clouds 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 to spin more.

This is the stage where it will either develop into a mature cyclone or either loose its momentum. Even if it has developed into a mature cyclone it can still grow and increase in wind speed and once they move over land their strength is weakened and they begin to fade, this is caused by a lack of moisture on land and heat compared to the ocean over which the cyclone formed.

Cyclone season is between November and April, the coastal regions of Queensland, Northern Territory and Western Australia are at risk of these cyclones.

The BoM issues cyclone warnings when said cyclone is expected to hit within 24 hours, and these warnings include areas which are likely to be affected, the name of the cyclone, its position, intensity and severity and movement.

The stages of a Tropical Storm go from a Tropical Depression, to a Tropical Storm, to a Tropical Cyclone to a Cat 5 Tropical Cyclone.

There are 5 categories to describe cyclones.

> Category 1 - Wind gusts less than 125km/hr

> Category 2 - Wind gusts 125 to 169km/ph

> Category 3 - Wind gusts 170 to 224km/ph

> Category 4 - Wind gusts 225 to 279km/ph

> Category 5 - Wind gusts more than 280km/ph

There is more than just wind damage that a cyclone can cause, such as flooding rains, which can cause further damage to property and increases the risk of people drowning. Cyclones also bring storm surges, which can damage buildings and cut off evacuation routes and cause injuries and death. Though most deaths from cyclones are from drowning, many lives are lost due to collapsing buildings or flying debris which can become extremely lethal in high winds.

How do cyclones get their name?

Each year, the BoM (Bureau of Meteorology) comprises a list of names for each year, they start at the top of the list and take it in turns to be a male or female name.

East Coast Lows

An East Coast Low (ECLs) are intense low-pressure systems which occur on average several times a year off the east coast of Australia, in particular southern Queensland, New South Wales and eastern Victoria, although they can occur at any time of year they are more common during autumn and winter with a max frequency of happening in June. ECLs will often intensify rapidly overnight making them one of the more dangerous weather systems to affect the NSW coast. ECL's are also seen off the coast of Africa and American and are sometimes known as east coast cyclones.

ECLs may form in a variety of situations, in summer they can be ex-tropical cyclones, at other times of year they will most often develop rapidly offshore with a pre-existing trough of low pressure due to favourable conditions in the upper atmosphere. ECLs may also develop in the wake of a cold front moving from Victoria into the Tasman Sea.

Gales and heavy rain occur on and near the coast south of the low centre, while to the north of the low can be clear skies, which can prove a challenge for forecasters is predicting the location and the movement of the centre of the low.

ECLs can generate one or more of the following:

> Gale or storm force winds along the coast and adjacent waters.
> Heavy widespread rainfall leading to the flash and/or major flooding.
> Very rough seas and prolonged heavy swells over coastal and ocean waters which can cause damage to the coast line.

Falling trees and flash flooding have caused fatalities on land and many small water craft have been lost off the coast and larger vessels have run aground during ECLs.

What is the difference between an ECL and a Tropical Cyclone?

Cyclones, as stated above, form over very warm tropical waters where the sea surface temperature is greater than 26C. They usually have long life cycles, typically lasting around a week and severe tropical cyclones (Cat 3 or greater) can produce significant damage with their wind speeds over 180kmph near the centre, heavy rainfall and coastal inundation through storm surgers. Tropical Cyclone "Justin" which affected QLD in March 1997, lasted 18 days.

ECL's on the other hand have much shorter lifespans than tropical cyclones and last only a few days. They develop over the Tasman sea close to the NSW coast and can intensify over the 24hr period. Unlike tropical cyclones where warm seas provide their energy, ECLs are driven by a temperature gradient between the Tasman sea air and cold air in the high levels of the atmosphere over the continent.

While wind speeds recorded are lower than in severe tropical cyclones, a gust of 165kmph was recorded at Newcastle NSW with an ECL that sunk the bulk carrier Sygna in 1974, and during one of the first ECL's in June 2007, when the bulk carrier the Pasha Bulka ran around in a gust of 105km/ph at 6:21am on 8th June.

Safety tips for before and during a cyclone:

> Compile a list of emergency phone numbers and keep it visible to all family members.
> Nominate an interstate family member or friend to be a point of contact in case you or your family become separated during a cyclone.
> Find out if your home is located in an area that could be prone to storm surges or flooding by contacting your local council.
> Identify the strongest part of the house (usually the smallest room) and ensure everyone knows where this is in case you need to seek shelter in your home.
> Ensure at least one person in your household knows first aid.
> Prepare an emergency kit.
> Contact your local council to check if your home has been built to cyclone standards.
> Check your home and contents insurance.
> Check the condition of your roof and repair any lose tiles, eaves or roof screws.
> Ensure windows are fitted with shutters or metal screens.
> Trim any branches overhanging your house.
> Clear gutters of leaves and debris.

Before a cyclone:

> Listen to your portable radio and watch for BoM warnings on the BoM website. (
> Locate and check your emergency kit.
> Check that your neighbours are aware that a cyclone watch or warning has been issued.
> Clear your property of all loose items.
> Secure any boats and caravans and move vehicles under cover.
> Fill buckets and bath with water in case the water supply becomes restricted, ensure you have sufficient water purification tablets to make the water drinkable.
> Prepare an evacuation kit.
> Withdraw a sufficient amount of cash to cover essential items, place this in your evacuation kit.
> Close shutters on windows, or tape windows in a criss-crossing fashion using strong packing tape, this may not stop shattering of glass but will help hold the broken glass in place, you can also board or block windows.
> Bring kids and pets indoors and remain inside until further advice is given.

During a cyclone:

> Turn off all power, gas and water and unplug all appliances.
> Keep your emergency kit close at hand
> Bring your family into the strongest part of your house
> Keep listening to the radio for cyclone updates and remain indoors until advised.
> If the building begins to break up, immediate seek shelter under a strong table or bench or under a heavy mattress.
> BEWARE THE CALM OF THE EYE OF THE CYCLONE. - Stay inside until you have received official advice that it is safe to go outside.
> If an official evacuation order is issued then you and your family must leave your home immediately and seek shelter with friends or family who are further inland or on higher ground
> If you are visiting or holidaying in cyclone prone area and do not have family or friends to shelter with, contact your accommodation manager to identify options for evacuation.

Image is Cyclone Yasi.