Thunderstorm Outlook
Issued at 7:43am 28/08/2026
Valid from 7:43am 28/08/2026 to Midnight 28/08/2026
Bands of showers in a northwest flow continue to bring a low risk of thunderstorms to Westland, Grey, Buller and northwest Tasman until mid-afternoon. At night, a trough is forecast to move onto the southwest of the South Island from the west, bringing a low risk of thunderstorms to Fiordland south of George Sound and Stewart Island. There is minimal risk of thunderstorms or significant convection elsewhere in New Zealand during this period.
Issued at 7:59pm 28/08/2026
Valid from Midnight 28/08/2026 to Midday 29/08/2026
Chart reviewed at 8pm Friday and no changes made. A low approaches Northland during Saturday morning. A warm and humid airmass is dragged southwards and brings some instability through the region. There is a low risk of thunderstorms from before dawn, with a low risk of localised downpours (25-40 mm/h) from late morning as indicated on the chart. A trough moves through the lower South Island before dawn and there is a low risk of thunderstorms associated with this trough. There is minimal risk of thunderstorms or significant convection elsewhere in New Zealand during this period.
Issued at 9:43am 28/08/2026
Valid from Midday 29/08/2026 to Midnight 29/08/2026
The low moves southwards over the upper North Island during the afternoon. The associated airrmass is warm and humid, especially for late winter and is conducive to a low risk of thunderstorms with a low risk of localised downpours (25-40mm/h). The risk gradually shifts southeastwards during the second half of the day, affecting the Auckland region during the evening and early part of the night as indicated on the chart. A front moves onto the south of the South Island in the evening bringing a low risk for Fiordland. Behind the front the atmosphere remains unstable and cold and the low risk continues in showers at night for the region indicated. There is minimal risk of thunderstorms or significant convection elsewhere in New Zealand 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.
