Thunderstorm Outlook
Issued at 4:01pm 18/08/2026
Valid from 4:01pm 18/08/2026 to Midnight 18/08/2026
Chart updated at 4PM to extend a low risk to the ranges of northern Hawke's Bay. From afternoon onwards, a strong cold south to southwest flow, and very cold temperatures aloft, bring more frequent showers to the east coast of the North Island. About the coastal areas of Gisborne/Tairawhiti, including Mahia Peninsula, also the ranges of northern Hawke's Bay, there is a low risk of one or two thunderstorms. Any thunderstorms here are likely to bring strong gusts and small hail. Although not shown on the chart, there is a low risk of thunderstorms for Chatham Islands during the late afternoon and evening where there is also a risk of small hail. No thunderstorms or significant convection expected elsewhere during this period.
Issued at 7:07pm 18/08/2026
Valid from Midnight 18/08/2026 to Midday 19/08/2026
A strong cold south to southwest flow brings frequent showers to the east coast of the North Island during the morning, and eases during the day. There is a low risk of a few thunderstorms before dawn and during the morning about coastal areas of Gisborne/Tairawhiti and Hawke's Bay, also the Wairoa District. Any thunderstorms here are likely to bring strong gusts and small hail. No thunderstorms or significant convection expected elsewhere during this period.
Issued at 8:29am 18/08/2026
Valid from Midday 19/08/2026 to Midnight 19/08/2026
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.
