Thunderstorm Outlook
Issued at 7:22am 11/09/2026
Valid from 7:22am 11/09/2026 to Midnight 11/09/2026
Several fronts and troughs move over New Zealand, embedded in a cool southwest flow. There is a low risk of one or two thunderstorms about Stewart Island and the coastal areas of Clutha late morning and early afternoon, and then again at night. The risk of thunderstorms or severe convection is minimal elsewhere.
Issued at 10:02am 11/09/2026
Valid from Midnight 11/09/2026 to Midday 12/09/2026
A trough brings a low risk of one or two thunderstorms with hail to coastal Clutha before dawn. Not indicated on the chart, there is a moderate risk of thunderstorms for the Chatham Islands late morning. Thunderstorms will bring localised heavy rain and hail. The risk of thunderstorms or severe convection elsewhere 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.
