Thunderstorm Outlook
Issued at 7:32am 19/09/2026
Valid from 7:32am 19/09/2026 to Midnight 19/09/2026
A cold front is forecast to move northwards over southern New Zealand later today, followed by a strong and unstable west to southwest flow. From this afternoon through to night, there is a moderate risk of thunderstorms for Fiordland south of Milford Sound, Stewart Island and coastal Southland, and then remaining southern parts of Southland, southern and eastern Clutha and southern Banks Peninsula in the evening and at night as depicted on the chart. Thunderstorms that occur may be squally with strong wind gusts of 90 to 110 km/h, produce brief heavy rain with intensities of 5 to 10 mm/h, and small hail. There is a low risk of thunderstorms that extends northwards to include the remainder of Fiordland, the Westland District, much of Otago, and coastal South Canterbury north of Ashburton to northern Banks Peninsula this evening and tonight, as depicted on the chart. There is minimal risk of thunderstorms or significant convection elsewhere during this period.
Issued at 7:28pm 19/09/2026
Valid from Midnight 19/09/2026 to Midday 20/09/2026
A cold front moves northwards from Canterbury to Gisborne during the morning, followed by a cold and unstable southwest flow. There is generally a low risk of thunderstorms for the southern South Island, mid-Canterbury near the coast, and southern and eastern parts of the North Island, as depicted on the chart. However, the risk of thunderstorms is considered moderate for Clutha and Banks Peninsula in the few hours after midnight Saturday, and for the southeast of Wairarapa before dawn. These thunderstorms may produce brief heavy rain, small hail, and strong wind gusts of 80 to 100 km/h. Also, although not depicted on the chart, there is a low risk of thunderstorms for the Chatham Islands during the morning. There is minimal risk of thunderstorms or significant convection elsewhere in New Zealand during Sunday morning.
Issued at 8:57am 19/09/2026
Valid from Midday 20/09/2026 to Midnight 20/09/2026
There is minimal risk of thunderstorms or significant convection during this period.
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 25mm/h, or more.
Large hail:
Hailstones 20mm in diameter, or larger.
Strong wind gusts (from thunderstorms):
Gusts of 110km/h (60 knots) or stronger.
Damaging tornadoes:
Fujita F1 - i.e. wind speeds greater than 116km/h (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.
