Thunderstorm Outlook
Issued at 7:49am 1/09/2026
Valid from 7:49am 1/09/2026 to Midnight 1/09/2026
There is minimal risk of thunderstorms or significant convection during this period. A strong cold southwesterly flow over much of the country eases today as a ridge builds from the Tasman Sea. Although not depicted on this chart, there is a moderate risk of thunderstorms for the Chatham Islands until evening, bringing gusts of around 100 km/h and small hail.
Issued at 7:15pm 1/09/2026
Valid from Midnight 1/09/2026 to Midday 2/09/2026
A showery northwest flow spreads onto the western areas of the South Island during the morning and there is a low risk of thunderstorms for southern Westland, Fiordland and Stewart Island. There is minimal risk of thunderstorms or significant convection elsewhere during this period.
Issued at 9:08am 1/09/2026
Valid from Midday 2/09/2026 to Midnight 2/09/2026
A showery northwest flow continues to spread onto the western areas of the South Island during the second half of Wednesday. There is a low risk of thunderstorms for southern Fiordland and Stewart Island during the afternoon and for northern Fiordland and the Westland District during the afternoon and evening. 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.
