A cyclone is a large scale air mass that rotates around a strong centre of low atmospheric pressure. There are 4 main categories of large synoptic scale cyclones. 

 

• Tropical cyclone - Originates in the tropics between 5° to 23° south of the equator. Non frontal, warm core.

• Subtropical cyclone - Originates between 23° to 50° south of the equator. Non frontal, warm core.

• Extratropical cyclone - Originates between 23° to 60° south of the equator. Frontal, cold core.

• Polar low - Originates between 60° to 90° south of the equator. Frontal, cold core.

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Examples of a smaller scale cyclone is a waterspout, tornado, mesocyclone, dust devil and fire twister. 

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Of the 4 large scale cyclones, only subtropical and extratropical cyclones have a direct impact on the upper North Island of New Zealand. Regional met agencies name a tropical cyclone which retains it's name when it transitions beyond the tropics into New Zealand waters.

 

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