The air pressure at sea level drops dramatically and causes more wet air to be sucked into the heights. A whirl is forming like in a tornado, but even larger. The diameter may reach up to 1500 miles, the wind speed up to 180 mph. In the centre of the whirl the air is sinking again to form a cloudless 'eye'. In the Atlantic ocean these tropical cyclones are called 'hurricanes', the Chinese say 'taifun', the Indians call it 'cyclone' and the Australian people 'willy-willy'.
Cyclones can only move freely across the sea.
When they reach the shore, they are stopped by the lack of the wet warm air supply and the uneven surface. Most of the time, the wind speed decreases to a 'gentle breeze'. Hurricane wind speed belongs to scope 12 at the Beaufort scale. Scope 12 is the end of this scale. So a new scale, the Saffir-Simpson scale, was developed for tropical depressions.