Thunderstorm Outlook
Issued at 8:15am 25/10/2026
Valid from 8:15am 25/10/2026 to 1:00am 26/10/2026
There is minimal risk of thunderstorms or significant convection during this period.
Issued at 8:17pm 25/10/2026
Valid from 1:00am 26/10/2026 to 1:00pm 26/10/2026
A strong cold front approaches the South Island Monday morning. Ahead of this front there is a warm and humid airmass that becomes marginally unstable. There is a low risk of thunderstorms for Fiordland and Stewart Island as indicated on the chart.
Issued at 8:45pm 25/10/2026
Valid from 1:00pm 26/10/2026 to 1:00am 27/10/2026
The front moves northwards over the South Island during the second half of Monday. The preceding airmass remains warm and humid as well as marginally unstable. With strong orographic forcing there is a low risk of thunderstorms, but the main factor with this event will be high intensity heavy rain with peak rainfall rates of 25-35 mm/h. Please note heavy rainfall warnings are in place for western parts of the South Island.
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.
