Severe Thunderstorm Criteria
In New Zealand, MetService classifies a thunderstorm as severe if one or more of the following criteria are met:
- Heavy rain (from thunderstorms):
- Rainfall of 25 millimetres per hour, or more.
- Large hail:
- Hailstones 20 millimetres in diameter, or larger.
- Strong wind gusts (from thunderstorms):
- Gusts of 110 kilometres per hour / 60 knots or stronger.
- Damaging tornadoes:
- Fujita F1 (wind speeds greater than 116 kilometres per hour / 63 knots) or stronger.
Note: some tornadic systems such as funnel clouds, waterspouts and small land-based tornadoes are possible with thunderstorms that may not be classified as severe.
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