Cyclones

 

Tropical Cyclones, known as ‘hurricanes’ in the Americas and typoons across Asia, form over warm ocean waters and require a sea surface temperature of at least 27C to get started. Tropical cyclones are intense low-pressure cells of tropical origin, and they are capable of generating tremendously strong winds and heavy rain across a large area. The centre of these systems is called the eye – a clear area of light winds surrounded by raging tempests that can produce wind gusts up to 300 kph. The eye is normally around 50 km across but can be larger or smaller depending on the nature of the cyclone. The eye is surrounded by towering walls of cloud that extend up to 15 km into the sky.

 

 

Tropical cyclones are categorised by their intensity which is based on the strength of the winds they generate. Five categories are used in Australia (1 to 5) with Category 1 the weakest end of the spectrum. Cyclones of category 3 or above are termed severe tropical cyclones.

 

Category 1:

Wind gusts between90 and 125 kph - Gale force winds;

Minor damage to houses – roof tiles displaced; small tree branches down.

 

Category 2:

Wind gusts between 125 - 164 kph - Destructive winds;

Some house damage – wooden fences down, small trees blown over

 

Category 3:

Wind gusts between165 - 224 km/h - Very destructive winds;

House roofs lose tiles and shutters; power failures and big trees down.

 

Category 4:

Wind gusts between225 - 279 km/h - Highly destructive winds; Roofs torn off, many trees down, widespread power failure; dangerous airborne debris thrown great distances.

 

Category 5:

Wind gusts more than 280 km/h - Extremely destructive winds;

Widespread destruction of houses and devastating damage across a wide area.

 

 

The tropical northern coastline of Australia is an area highly prone to tropical cyclone activity, with these often massive storm systems posing a constant threat to the area, particularly between the months of November and April – the cyclone season.