Issued at 8:20am 5/09/2025

Valid from 8:20am 5/09/2025 to Midnight 5/09/2025

An unstable northwest flow covering the South Island tends colder southwest during the second half of today. An embedded front moves northwards over the northern South Island and onto the southern North Island in the evening. This morning and afternoon, there is mostly a moderate risk of thunderstorms embedded within broader areas of rain over Westland north of the Glaciers, Grey, Buller, Kahurangi National Park, the Nelson Lakes area, and also Canterbury high country areas near the Divide, with localised heavy rain of 10-25 mm/h, small hail, and strong wind gusts of 90 km/h, with one or two small tornadoes also possible about the west coast. However about the ranges of Westland and Grey this morning and about the ranges of Buller this morning and afternoon, the risk of thunderstorms is high, with the additional risk strong wind gusts could reach 110 km/h. There is also a moderate risk of thunderstorms about southern Westland, Fiordland, southern Southland, Clutha and Stewart Island through much of the period. These thunderstorms bring strong winds gusts of 80-90 km/h, brief heavy rain and hail, with snow lowering to 400 metres in the south during the period. Elsewhere, a low risk of thunderstorms affects many other northern, western and southern parts of the South Island as indicated on the chart, and also about Taranaki tonight. No other thunderstorms or significant convection expected over New Zealand during this period.

Issued at 9:12pm 5/09/2025

Valid from Midnight 5/09/2025 to Midday 6/09/2025

Chart reviewed Friday 7:45pm and moderate risk areas added to Great Barrier Island, eastern Bay of Plenty, Horowhenua and Kapiti. Several fronts affect the North Island Saturday morning, bringing a mostly low risk of thunderstorms to areas in the west from Northland to Kapiti and across Coromandel Peninsula and Bay of Plenty. However, for much of Northland and Great Barrier Island the risk increases to moderate for a time. Any thunderstorms that occur could bring localised heavy rain of 25 mm/h and possibly greater. There is also a moderate risk of thunderstorms about Horowhenua and Kapiti for a time around dawn, and about eastern Bay of Plenty late morning. For Horowhenua and Kapiti, localised heavy rain of 5 to 15 mm per hour and small hail are possible. For eastern Bay of Plenty, localised rain rates of 15 to 25 mm per hour are possible. A deeply cold unstable air mass affects the South Island. There is moderate risk of thunderstorms in northern Westland, Grey, Buller and the west of the Tasman District before dawn and for Fiordland, southern Southland including Stewart Island, and Clutha throughout the morning. For these areas localised heavy rain with intensities of 5 to 15 mm per hour and small hail are possible. There is a lower risk of thunderstorms for remaining western and eastern areas of the South Island. For the rest of New Zealand there is a minimal risk of thunderstorms.

Issued at 7:50pm 5/09/2025

Valid from Midday 6/09/2025 to Midnight 6/09/2025

Chart reviewed Friday 7:50pm and no changes made. An active squally front is expected to move north over the southern South Island from late afternoon and during the evening, and is forecast to bring a moderate risk of thunderstorms to Fiordland the south of Southland including Stewart Island, and Clutha. A lower risk extends to the south of Westland, inland Southland, and Dunedin. These thunderstorms if they occur area expected to bring heavy rain of 10 to 15 mm/h, small hail, and squally winds gusting 90 to 110 km/h. There is also a low risk of thunderstorms for the Kaikoura Coast, Wellington and Wairarapa in the afternoon. The risk of thunderstorms or significant convection is minimal for the rest of New Zealand during this period.