TROPICAL cyclones are intense low-pressure systems that form over warm tropical waters.
Winds in a cyclone travel in a clockwise direction around the centre and can reach speeds over 200kmh. The severe winds can extend for hundreds of kilometres from the calm "eye" or centre of the cyclone.
Cyclones are dangerous because they produce destructive winds, heavy rainfall and damaging storm surges.
The destructive winds can cause extensive damage to property and vegetation and can turn debris into dangerous missiles.
The heavy rainfall associated with cyclones can produce extensive flooding and landslides which can cause property damage, increase the risk of drowning and cut road access.
Extreme waves generated by cyclones can cause severe coastal erosion and are dangerous to vessels out at sea and those moored in harbours.
The most destructive and dangerous hazard associated with tropical cyclones is the local rise in sea-level known as "storm surge" which can cause inundation and flooding of low-lying coastal areas.
Storm surge and storm tide
Storm surge is generated by the low atmospheric pressure and gale force onshore winds experienced during a tropical cyclone.
As a cyclone approaches the coast, this mound of seawater is pushed onto shore and can appear as a rapid rise in sea level, up to several metres high, at least 50km wide and can last up to several hours.
The combination of storm surge and normal ocean tide is known as a "storm tide". The worst impacts can occur when a storm surge arrives on top of a high tide. When this happens, the storm tide can reach areas that might otherwise have been safe. If you live in a low-lying tropical or sub-tropical coastal area, you could be at risk from storm tide inundation.
Will you need to plan for evacuation?
Find out from your council if your home is in a storm tide evacuation area.
If it is, arrange a safer place for your evacuation as part of your preparations.
Ask friends or family that live in secure accommodation, in an area further inland and on higher ground if you can seek shelter in case of storm tide.
Storm tide can damage and destroy buildings, cut off evacuation routes and cause injuries and fatalities.
You put yourself and your family at great risk if you do not evacuate when requested.
If you don't live in a storm tide evacuation area, sheltering in place by staying in your home is often the best option.
However, if you live in an old home, built before 1982, or if you have special needs, it may be safer to stay with family or friends in a newer home.
A Cyclone Watch is issued by the Bureau of Meteorology when gales or stronger winds associated with a cyclone are expected to hit within 24-48 hours.
A Cyclone Warning is issued by the Bureau when gales or stronger winds are expected to hit within 24 hours.
When you hear a cyclone warning and it is safe to shelter in place:
- activate your emergency plan
- turn off all mains supply and unplug all appliances
- bring your family into the strongest part of the house (usually the smallest room in the house with the least windows)
- keep your emergency kit close at hand
- stay tuned into warnings via battery radio for updates
- stay away from glass windows and remain indoors until advised
- if the building begins to break up, immediately seek shelter under a strong table or bench or under a heavy mattress.
Beware the calm eye of the cyclone.
Some people venture outdoors during the eye of a cyclone, mistakenly believing that the cyclone has passed.
Remember to stay inside until you have received official advice that it is safe to go outside.
Update your news preferences and get the latest news delivered to your inbox.