Meteorological Information

• What are they
• When and where
• Life cycle
• Structure
• The Cyclone
  Threat
• Northern
  Territory
• Cyclone Tracy
• Warning System

Cyclone Tracy

Oral Histories

Front Page

Tropical cyclones are intense low pressure systems that form over tropical oceans with sustained winds exceeding gale force (63 km/h) surrounding the centre. Their circular wind pattern has a clockwise rotation in the Southern Hemisphere and counter-clockwise in the Northern Hemisphere. At lower latitudes (5⁰-10⁰) tropical cyclones tend to be small in size (sometimes less than 100 km in diameter) but in higher latitudes they typically grow to more than 1000 km and occasionally to more than 2000 km in diameter.

Severe tropical cyclones have maximum winds surrounding the centre exceeding hurricane force (120 km/h). In Asian countries bordering the Northwest Pacific severe tropical cyclones are called typhoons whilst in the USA and Caribbean they are known as hurricanes.