Thunderstorm Outlook
Issued at 7:37am 18/07/2026
Valid from 7:37am 18/07/2026 to Midnight 18/07/2026
A front and associated slow-moving rain band move northwards over the lower South Island. A low risk of thunderstorms spreads north across Fiordland, Southland and Clutha from late morning. For southern Fiordland, Southland and Clutha the risk subsides at night as winds turn southwest. Minimal risk of thunderstorms or significant convection for the rest of 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.
