Thunderstorm Outlook
Issued at 7:56am 20/06/2026
Valid from 7:56am 20/06/2026 to Midnight 20/06/2026
A front moves northwards over the central and northern South Island today. Heavy Rain Warnings and Watches remain in force for some western South Island areas, as well as the Tararua Range. There is a moderate risk of thunderstorms embedded within broader areas of rain about the ranges of Westland and Grey districts, and the Canterbury High Country near the main divide this afternoon and early evening. A low risk covers other western areas from Buller to coastal Westland and Grey, and remaining parts of the Canterbury High Country. Any thunderstorms that occur may boost local rainfall rates onto the 20-30 mm/h range. Another front then moves across Fiordland during the afternoon and evening with a low risk of thunderstorms. There is a minimal risk of thunderstorms or significant convection over the remainder of New Zealand during this period.
Issued at 8:08am 20/06/2026
Valid from Midnight 20/06/2026 to Midday 21/06/2026
A front moves northwards from Westland to Buller during the period, bringing showers, and a low risk of thunderstorms as depicted on the chart. There is a minimal risk of thunderstorms or significant convection over the remainder of New Zealand 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.
