Severe Weather Outlook

Issued: 10:25am Wednesday 6 Dec 2023

Valid Friday 08-Dec-2023

A ridge of high pressure should spread over New Zealand on Friday. No severe weather is expected over the country on Friday.

Valid Saturday 09-Dec-2023

A cold front is expected to move onto the southern South Island during Saturday bringing rain to western and southern South Island areas. A strong northwest flow precedes the front, and a lighter southerly flow follows it.
There is moderate or high confidence that northwesterly rain will reach warning criteria about central and southern Westland, Fiordland, and the Canterbury and Otago headwaters near the main divide. There is low confidence of warnable rainfall about northern Westland and the Paparoa Range.
There is also moderate confidence that northwest winds could reach severe gale about exposed parts of Fiordland and Southland (including Stewart Island), and low confidence about Otago and the Canterbury High Country.

Valid Sunday 10-Dec-2023

The front moves northwards over the northern South Island and southern North Island on Sunday.
There is moderate confidence that the warning amounts of rain about Westland and the Canterbury High Country near the main divide will continue into Sunday morning. There is low confidence of warnable rainfall amounts about Buller and western parts of Tasman.
There is also low confidence that northwest winds could reach severe gale about exposed parts of northern Canterbury, Marlborough, Wellington, Wairarapa and the Tararua District.

Valid Monday 11-Dec-2023

A weak ridge of high pressure should cover New Zealand on Monday. There is minimal risk of severe weather affecting the country on Monday.

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 Thursday, 07-Dec-2023

Issued: 8:14pm Wednesday 6 Dec 2023

Over the North Island, wind convergences are expected to develop showers about parts of the central North Island, including the Bay of Plenty, Thursday afternoon and evening, bringing a low risk of thunderstorms. Over the South Island, wind convergences are also expected to cause showers to develop about inland parts of Canterbury and North Otago Thursday afternoon and evening. There is a low risk of thunderstorms for the Canterbury High Country and inland North Otago during the afternoon and evening. No thunderstorms or significant convection expected elsewhere in 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.