Thunderstorm Outlook
Issued at 7:29am 23/08/2026
Valid from 7:29am 23/08/2026 to Midnight 23/08/2026
A series of fronts move across southern and central New Zealand this morning, and very cold air aloft moves over the lower South Island. During the second half of Sunday, the cold air aloft moves rapidly eastwards, and a very cold showery flow gradually stabilises. This morning and afternoon there is a moderate risk of thunderstorms over Westland, Fiordland, and also coastal Southland and Clutha. Any thunderstorms here could bring strong wind gusts of 90 to 110 km/h, possibly even more, and hail up to 10 mm diameter. A broader low risk extends farther east and north, as indicated on the chart. This morning, there is also a low risk of thunderstorms over the Marlborough Sounds, parts of Wellington and Horowhenua Kapiti Coast, and Taranaki. Not shown on the chart, there is also a moderate risk of thunderstorms over the Chatham Islands this evening and tonight, with gusts of 90 to 100 km/h and small hail likely. No thunderstorms or significant convection expected elsewhere during this period.
Issued at 7:40pm 23/08/2026
Valid from Midnight 23/08/2026 to Midday 24/08/2026
There is minimal risk of thunderstorms or significant convection during this period. Minimal risk of thunderstorms over Mainland New Zealand. However, before dawn Monday there is a moderate risk of thunderstorms over the Chatham Islands. Thunderstorms here could bring gusts of 90 to 100 km/h and small hail.
Issued at 7:28pm 23/08/2026
Valid from Midday 24/08/2026 to Midnight 24/08/2026
There is minimal risk of thunderstorms or significant convection 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.
