Tropical cyclones are weather extremes that can be life-threatening and highly destructive. If you’re planning to tour the tropics during the Wet, you’ll need to know about the risks and how to reduce your exposure.
The trick is not to be near a cyclone when it strikes the coast and the best tool for avoiding storms is using long-range weather forecasts.
If you’re planning to travel in the tropics during the cyclone risk months – October until May – it’s important to take advantage of the long-range forecast services such as the Bureau of Meteorology. However it’s well known that there’s nothing as changeable as the weather (discounting politicians). So it’s vital that you monitor weather forecasts constantly when in the tropics.
Cyclones form at sea and ‘feed’ on warm tropical waters, so they usually lose strength quickly as they move inland, becoming rain depressions. The risk of damaging winds decreases rapidly as such storms move inland, but the likelihood of flooding is high.
So if you’re threatened by a cyclone and decide to up stakes and head inland, make sure your destination offers protection from flooding. Heavy rainfall associated with the passage of a tropical cyclone can produce extensive flooding, hundreds or even thousands of kilometres from the storm centre, in the central and southern parts of the continent.
In the tropics, local authorities have introduced cyclone warning procedures. The storm early warning system (SEWS) is a wailing sound used throughout Australia for various emergencies of major significance, such as cyclones, flooding and severe storms. When you hear the signal on radio or television, pay careful attention to the message that follows and act immediately on the advice given.
Cyclone Watch: This is usually issued when gales associated with a tropical cyclone are expected to affect coastal or island communities within 48 hours. A Cyclone Watch will include an estimate of the cyclone’s position, its intensity, severity and movement. Cyclone Watches will be issued every three hours initially and hourly once the cyclone nears the coast.
Cyclone Warning: This is issued when the gales associated with a tropical cyclone will affect coastal or island communities within 24 hours. When a Cyclone Watch is issued it’s an excellent idea to move camp if your site is in the likely path of the storm. A 48-hour warning gives you ample time to move to a safer location – away from the coast is nearly always the best option.
What, exactly, is a cyclone?
Tropical cyclones build from low atmospheric pressure systems that form over warm tropical waters. They derive their energy from the warm oceans and don’t build unless the sea-surface temperature is above 26.5°C. However, once activated, a cyclone can ‘live’ over cooler waters and land for some time.
Cyclones can persist for a few days or up to three weeks and are difficult to predict in terms of direction and duration. Australian cyclones have more erratic paths than circular storms (hurricanes and typhoons) in other parts of the world. Generally, cyclones travel slowly, around 10-25km/h, but movement in any direction is possible, including sharp turns and even loops.
From a satellite, a cyclone is characterised by a distinctive swirling rotational cloud pattern around a central clear patch, or ‘eye’. Destructive winds can extend hundreds of kilometres from the cyclone centre. The circular eye or centre of a tropical storm ranges in size from under 10km to over 100km in diameter and is surrounded by a dense ring of cloud about 16km high that produces the strongest winds and heaviest rainfall.
It is important to remember that during the passage of the cyclone centre there is a temporary lull in the wind, but this is soon replaced by destructive winds from a different direction.
The destructive winds accompanying tropical cyclones produce phenomenal seas, in conjunction with seriously low atmospheric pressure that allows sea levels to rise. This so-called “storm surge” combines with normal tides to produce water heights that may be 2 to 5m higher than the mean high tide level in the area. What seems like high ground may be high risk.
Cyclones are rated by weather observers according to their intensity at any point in time. Constant monitoring of the storm’s intensity may result in a change in the cyclone’s category, which is why it’s important to keep in touch with authorities once a storm warning has been issued.
- Category 1 cyclones can damage caravans, with wind gusts of up to 125km/h. These winds correspond to Beaufort 8 and 9 (gales and strong gales).
- Category 2 cyclones can certainly cause serious caravan damage, thanks to wind speeds of up to 170km/h. These winds correspond to Beaufort Scale 10 and 11 (storm and violent storm).
- A Category 3 cyclone’s strongest winds are very destructive with gusts of up to 225km/h, which is an official hurricane of Beaufort 12 intensity.
- A Category 4 cyclone will almost certainly blow away an untethered caravan and may tear apart one that’s tied down. Debris may be blown around at lethal speeds in wind gusts of up to 280km/h.
- A Category 5 cyclone doesn’t bear thinking about.