Thunderstorm Outlook
Issued at 8:20am 21/04/2026
Valid from 8:20am 21/04/2026 to Midnight 21/04/2026
A trough crosses Northland and Auckland during the afternoon, bringing a moderate risk of thunderstorms then and during the early evening, as indicated on the chart. A low risk precedes the trough during the morning, mainly about western coastal areas. Any thunderstorms that occur will generate localised heavy rain, 10 to 25 mm per hour. In the east of the North Island, a front moves slowly northwards, generating showers and a band of rain. There is an associated low risk of embedded thunderstorms for northern Hawke's Bay, eastern Bay of Plenty and Gisborne. There is minimal risk of thunderstorms or significant convection elsewhere during Tuesday.
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.
