Weather
Thunderstorms have developed in Southland, Clutha and Central Otago this afternoon. Some of these thunderstorms are expected to bring heavy rain with intensities of 10 to 25mm per hour and hail 10 to 20mm in diameter.
Additionally there is a moderate risk that some slow moving thunderstorms could become SEVERE producing downpours with intensities of 25 to 40mm per hour. Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips. Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.
Should severe weather approach or if you feel threatened, take shelter immediately.
Note: A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms in and close to the watch area. People in these areas should be on the lookout for threatening weather conditions and monitor for possible Severe Thunderstorm Warnings.
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.
Source: Metservice