Thunderstorm Outlook
Issued at 7:34am 29/08/2026
Valid from 7:34am 29/08/2026 to Midnight 29/08/2026
A low moves southwards over the upper North Island during the afternoon. The associated airmass is warm and humid, especially for late winter. The risk of thunderstorms is generally considered low, but the airmass is conducive to a moderate risk of localised downpours (25-40 mm/h) over Northland, Auckland, Coromandel Peninsula and western Bay of Plenty as indicated on the chart. The risk gradually shifts southeastwards during the second half of the day, affecting the Auckland, Coromandel Peninsula and western Bay of Plenty during the evening and early part of the night and eastern Bay of Plenty at night, where the downpour risk is considered low. A front moves onto the south of the South Island in the evening bringing a low risk for Fiordland and parts of Southland. 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.
Issued at 7:46pm 29/08/2026
Valid from Midnight 29/08/2026 to Midday 30/08/2026
Chart reviewed at 7:45pm Saturday and low risk area extended further west across Bay of Plenty. A front and associated warm and humid airmass affects the northeast of the North Island before dawn on Sunday. There is a low risk of thunderstorms and low risk of downpours (25-40 mm/h) about southern Coromandel Peninsula and the Bay of Plenty. A strong cold and unstable southwest flow affects coastal Fiordland, Southland and parts of Otago. There is a low risk of squally thunderstorms with small hail wind gusts of 80 to 100 km/h as indicated on the chart. There is minimal risk of thunderstorms or significant convection elsewhere in New Zealand during this period.
Issued at 9:12am 29/08/2026
Valid from Midday 30/08/2026 to Midnight 30/08/2026
A strong cold and unstable southwest flow affects southern Fiordland, Southland and parts of Otago. From afternoon, this risk includes Banks Peninsula too. There is a low risk of squally thunderstorms with small hail wind gusts of 80 - 100 km/h as indicated on the chart. 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.
