Thunderstorm Outlook
Issued at 7:29pm 12/07/2026
Valid from 7:29pm 12/07/2026 to Midnight 13/07/2026
A front followed by an unstable showery air-mass moves east over the South Island during the second half of Monday. In Fiordland, there is a moderate risk of thunderstorms with heavy rain, 10 to 15 mm/h and strong wind gusts, 90 to 100 km/h. For Westland there is also a moderate risk of thunderstorms with heavy rain, 10 to 25 mm/h. There is a low risk of thunderstorms extending slightly farther east from these moderate risk areas, also including Stewart Island. In the evening and at night, there is a low risk of thunderstorms for Grey, Buller and the far west of Nelson as indicated on the chart. There is minimal risk of thunderstorms or significant convection elsewhere 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.
