Thunderstorm Outlook
Issued at 8:09am 20/07/2026
Valid from 8:09am 20/07/2026 to Midnight 20/07/2026
Strengthening troughs affect parts of the upper North Island today. There is a low risk of thunderstorms for all of Auckland and southern Northland, also coastal Waikato, as indicated on the chart. However, the risk is considered moderate around and over Great Barrier Island from afternoon and these thunderstorms will generate localised heavy rain with rainfall rates of 10 to 25 mm per hour. There is also a low risk of thunderstorms for eastern Coromandel Peninsula this morning and afternoon. There is minimal risk of thunderstorms or significant convection elsewhere today.
Issued at 9:19am 20/07/2026
Valid from Midnight 20/07/2026 to Midday 21/07/2026
The instability remains in the southeast flow over the upper North Island during the morning and there is a low risk of thunderstorms for the far north of Auckland, Great Barrier Island and coastal areas of eastern Northland as indicated on the chart during the morning. There is also a low risk of thunderstorms for southern Fiordland and Stewart Island from late morning. 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.
