Thunderstorm Outlook
Issued at 8:24am 26/10/2026
Valid from 8:24am 26/10/2026 to 1:00am 27/10/2026
A front moves northwards over the South Island during the second half of Monday. The preceding airmass is 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.
Issued at 7:50pm 26/10/2026
Valid from 1:00am 27/10/2026 to 1:00pm 27/10/2026
A cold front moves northwards from central Westland to the Tasman District before dawn and there is a low risk of thunderstorms. Much of this region is under a heavy rain warning. This front then moves onto the south and west of the North Island during the morning, bringing a low risk of thunderstorms as depicted on the chart. Additionally, there is another cold front that moves through Southland and Otago before dawn. With and behind this front there will be showers, with a low risk of thunderstorms and some small hail. No thunderstorms or significant convection elsewhere in New Zealand.
Issued at 10:38am 26/10/2026
Valid from 1:00pm 27/10/2026 to 1:00am 28/10/2026
The cold front continues to move northeast across the North Island in the afternoon. Ahead of this front there is a low risk of thunderstorms in a rain band. The risk is considered moderate however with a southerly change that moves through Hawke's Bay in the afternoon with daytime heating increasing the instability. These storms could bring some heavy rain of 10-25 mm/h. The showery flow over Southland and Otago gradually eases, but there remains a low risk of thunderstorms with small hail until late afternoon. Finally, the upper atmosphere gradually cools over much of the South Island tomorrow, and there is some low level convergences that set up in response to daytime heating through the Canterbury foothills. Here the thunderstorm risk is assessed as low with the possibility of small hail as indicated on the chart. No thunderstorms or significant convection elsewhere in New Zealand.
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.
