Severe Weather Outlook

Valid from Saturday 05-Dec-2020 to Tuesday 08-Dec-2020

Issued: 2:09pm Thursday 3 Dec 2020

A trough should move across New Zealand on Saturday, followed by a ridge of high pressure on Sunday.

Sunday night, a front is expected to approach from the west, moving up the South Island during Monday, then becoming slow-moving over central New Zealand on Tuesday. Rain is forecast to affect western areas, and northwest winds could rise to gale in eastern parts.

On Monday and Tuesday, for the South Island west coast, there is generally low confidence of rainfall accumulations meeting warning criteria, but moderate confidence on Monday about Westland and Buller. There is moderate confidence of significant heavy rain for the Tararua Range, and low confidence for Mt Taranaki.

In addition, there is a low confidence of severe northwest gales about inland parts of Southland, Fiordland, Otago and Canterbury, and also about Wellington and the Wairarapa from late Sunday to Tuesday.

Low confidence:

a 20% likelihood (or 1 chance in 5) that the event will actually happen.

Moderate confidence:

a 40% likelihood (or 2 chances in 5) that the event will actually happen.

High confidence:

a 60% likelihood (or 3 chances in 5) that the event will actually happen.

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

Thunderstorm Outlook

Valid to Midnight Thursday, 03-Dec-2020

Issued: 7:12am Thursday 3 Dec 2020

A front is moving northwards across Waikato and Auckland this morning, with a low risk of a few elevated thunderstorms. No thunderstorms or severe convection expected over the remainder of New Zealand.



Valid to Noon Friday, 04-Dec-2020

Issued: 8:03pm Thursday 3 Dec 2020

An unstable northwest flow affects the southwest of the South Island, bringing periods of heavy rain to Fiordland and South Westland along with a moderate risk of thunderstorms. These thunderstorms may produce localised rainfall rates of 10 to 25mm/hr and small hail. A low risk of thunderstorms extends over Stewart island, and the far west of Southland and Otago. No thunderstorms or significant convection expected elsewhere during this period.



Valid to Midnight Friday, 04-Dec-2020

Issued: 8:08pm Thursday 3 Dec 2020

An unstable northwest flow persists across the west of the South Island through the second half of Friday. The trough should move across Westland in the afternoon with a burst of heavy rain and a moderate risk of thunderstorms, while a low risk of thunderstorms persists in Fiordland. In the evening, temperatures aloft over Fiordland cool further, and the risk of thunderstorms there becomes moderate. These thunderstorms may produce localised rainfall rates of 10 to 20mm/hr and small hail. A low risk of thunderstorms extends over Stewart Island, and also far western parts of Southland, Southern Lakes and Canterbury High Country. Afternoon and early evening wind convergence should produce showers over Dunedin, North Otago, and the far south of Canterbury, and there is a low risk of thunderstorms in this area. No thunderstorms or significant convection expected elsewhere 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.