Severe Thunderstorm Criteria
MetService uses the following criteria for severe thunderstorms in New Zealand:
- 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.
