Thunderstorm Outlook
Issued at 6:46am 27/08/2026
Valid from 6:46am 27/08/2026 to Midnight 27/08/2026
There is minimal risk of thunderstorms or significant convection during this period.
Issued at 7:16pm 27/08/2026
Valid from Midnight 27/08/2026 to Midday 28/08/2026
A front over the Tasman Sea moves onto the South Island during the morning. There is a low risk of thunderstorms associated with the front and in bands of showers that follow the front, affecting Fiordland before dawn, Westland from the glaciers southwards throughout the morning, and for Westland north of the glaciers, Grey, Buller and northwest Tasman after dawn, as depicted on the chart. There is minimal risk of thunderstorms or significant convection elsewhere in New Zealand during Friday morning.
Issued at 10:41am 27/08/2026
Valid from Midday 28/08/2026 to Midnight 28/08/2026
A front moving south towards the North Island is expected to be preceded by some unstable air. There is a low risk of thunderstorms for northern and eastern Northland from mid to late afternoon. Elsewhere, the risk of severe convection or thunderstorms is minimal.
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.
