natural disasters and cyclones

How do cyclones occur or form?

The formation of a cyclone has a number of stages

Stage 0 (Zero)- The right place and the right sea temperature is needed.

• The place is usually within + or - 5¡ã to ¡ã15 Lattitude from the equator over the ocean.
• The surface temperature of the ocean/sea needs to be 26.5¡ãC or above.
• A low airpressure system (depression) with convection currents starts to gather clouds/stormy

Stage 0 is basically continuous cloud build up even during the night time. The sun sun helps to heat the ocean and produces water vapour that forms couds.

 

Stage I is linked with a low air pressure system that starts to pull clouds in and rotate. It's not quite a cyclone but pretty likely.

 

Stage II is at the stage when the clouds start to really rotate but there is sometimes a chance that it may not develop in to a full cyclone.

After stage II the cyclone is mature and developed, it may increase in size or decrease. It can be in it's full maturity stage. (image of TC Bonnie /NASA)

 

The cyclone seasons The northern hemisphere is: June - November The southern hemisphere is: November -May

How do cyclones progress?

Often once the cyclone starts out small and starts to grow larger as it moves towards the north or south.

Destructive Cyclones don't last more than a few days as their energy runs out. Although it can pick up energy as it travels across warm water.

The low air pressure tends to 'drag' material around, eg clouds and moisture from the ocean.

Predicting the direction of a cyclone is very difficult for more than a few hours ahead in time. They can sometimes change direction very quickly(doing a hair pin turn) or just move in fairly straight line.

When a cyclone moves overland they usually lose most of their energy but can cause floods.

How are cyclones classified? The more common scale is the one for measuring typical likely damage. This is based on the Saffir-Simpson Hurricane Scale Category Wind gust speed/ Swell Damage 1 less than 125km/h 1.2-1.6m mild damage 2 126-169km/h 1.7-2.5m significant damage to trees 3 170 - 224km/h 2.6 -3.7 structural damage, power failures likely 4 225 - 279 km/h 3.8-5.4 most roofing lost 5 more than 280 km/h more than 5.4m almost total destruction Cyclones are classified based on information from satellite images and uses a scale called the Dvorak Number going from 0 to 8. References: BoM Cyclone Survival Handbook Other wind scales including beaufort and Dvorak A great diagram/animation of the type of damage cyclones cause.