When Super Typhoon Megi hit the headlines we were asked what is the difference between a typhoon a hurricane and a cyclone.

• Tropical Cyclones – form in the Southern Hemisphere (cyclonic)
• Hurricanes – form around America – either in the Atlantic Ocean or in the eastern Pacific Ocean (east of the International Dateline)
• Typhoons form in the western Pacific (west of the International Dateline).  This means a Hurricane that moves through the International Dateline would then become a Typhoon.

• Step 1:  A tropical ‘wave’ is needed.  This is literally a wave in the air, or a disturbance or the normal easterly flow.  The wind tries to move another direction and it causes the air pressure to start falling – and the air to start spinning – creating a low.
   
• Step 2:  This then forms into a tropical depression.   It’s given a number.  For example, TD2 (for the second Tropical Depression of the official storm season).
   
• Step 3:  Wind speeds start to average gale force – officially making it a Tropical Storm.  It’s at this point the storm is named.  In our part of the world this would become a Category 1 cyclone.
   
• Step 4:  There are some more technical things that need to go on, but once the winds increase we start stepping up the categories.  Different regions use different ways to measure a storm’s strength which is a bit of a pain – but this cyclone season (which starts in November and runs until April) we will use the category system used by the Bureau of Meteorology (BOM) in Australia – who really are the cyclone experts in the South Pacific.

Homepage image / File, Flooding from a typhoon in the Philippines last year / Rew Shearer