Thunderstorm Outlook
Issued at 8:50pm 20/04/2026
Valid from 8:50pm 20/04/2026 to Midnight 21/04/2026
In the afternoon, a trough affects Northland and Auckland. Here models indicate good instability and the thunderstorm risk during the afternoon and evening has now been increased to moderate with rainfall rates of 10 to 25 mm/h. A front moves northwards over the central and eastern North Island. There is an associated low risk of thunderstorms from Coromandel Peninsula and Waikato southeastwards to Hawke's Bay, as indicated on the chart. Generally, this risk is in the afternoon and evening, but also at night for Hawke's Bay. There is minimal risk of thunderstorms or significant convection elsewhere during this period.
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.
