Severe Weather Outlook

Issued: 10:54am Friday 4 Oct 2024

Valid Sunday 06-Oct-2024

A strong northwest flow is expected to affect the country, bringing rain to western areas, and northwest gales in exposed places. A low moving east may cross over the northern South Island late in the day.

There is low confidence that rainfall accumulations will meet warning criteria over Mount Taranaki/Taranaki Mounga and east to Tongariro National Park, the Tararua Range, western Tasman and the Buller District.

There is moderate confidence that the northwest winds will reach severe gale force about Wairarapa, including the Tararua District, Wellington and the Marlborough Sounds, and low confidence about inland Marlborough and Canterbury.

Valid Monday 07-Oct-2024

Northwesterlies continue over much of the country. A front is expected to be approaching the south of the South Island in the evening.

There is low confidence that rainfall accumulations will meet warning criteria over Mount Taranaki/Taranaki Mounga, the Tararua Range, Fiordland and the ranges of the Westland District.

There is moderate confidence that the northwest winds will reach severe gale force about Wairarapa, including the Tararua District, Wellington and the Marlborough Sounds.

Valid Tuesday 08-Oct-2024

A strong west to northwest flow over the country should turn southwest over the South Island during the day as an active front moves northwards.

There is moderate confidence that warning amounts of rain will fall in Fiordland, the ranges of Westland and the headwaters of the Otago and Canterbury lakes and rivers.

There is low confidence that west to northwest gales could become severe over Wellington, Wairarapa, the Tararua District, Central Hawke's Bay, Marlborough and inland Canterbury. There is also low confidence that westerlies about Stewart Island and the southern South Island will reach warning strength.

Valid Wednesday 09-Oct-2024

A weakening front is expected to cross over the North Island during the day, spreading a southwest flow over the country.

Some rain is likely with the front, but there is minimal risk that warnings will be needed.

Low confidence:

A 20% likelihood (or 1 chance in 5) of a warning being issued.

Moderate confidence:

A 40% likelihood (or 2 chances in 5) of a warning being issued.

High confidence:

a 60% likelihood (or 3 chances in 5) of a warning being issued.

New issues of this forecast are made available on this site at or before 16:30 NZST

Thunderstorm Outlook

Valid to Midnight Saturday, 05-Oct-2024

Issued: 8:24pm Friday 4 Oct 2024

An unstable northwest flow will cover northern and central New Zealand during the second half of Saturday, with bands of rain, heavy showers and possible thunderstorms affecting many areas. There is a moderate risk of thunderstorms affecting northern and western parts of the North Island from Northland to Horowhenua, including western Bay of Plenty, during the afternoon and evening, and about eastern Bay of Plenty and northern Gisborne/Tairawhiti from late afternoon into the night. A low risk covers many other parts of the North Island, and also Marlborough, Tasman/Nelson, inland North Canterbury and Westland. The low risk continues about northern and western parts of the North Island at night. These thunderstorms will bring localised heavy rain of 10-25mm/h, and small hail. There is also a low risk of one or two thunderstorms late afternoon and evening about about inland parts of central and south Canterbury, eastern Central Otago, far western Dunedin, inland parts of Clutha and Southland, and southern Fiordland. Also, although not depicted on the chart, there is a low risk of a few thunderstorms at the Chatham Islands on Saturday evening. No other thunderstorms or significant convection expected over 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 25 millimetres per hour, or more.

Large hail:

Hailstones 20 millimetres in diameter, or larger.

Strong wind gusts (from thunderstorms):

Gusts of 110 kilometres per hour / 60 knots or stronger.

Damaging tornadoes:

Fujita F1 (wind speeds greater than 116 kilometres per hour / 63 knots) or stronger.