Severe Weather Outlook

Valid from Monday 22-Jan-2018 to Thursday 25-Jan-2018

Issued: 02:01pm Saturday, 20-Jan-2018

A trough is expected to cross the North Island on Monday and Tuesday bringing outbreaks of rain over northern and central areas, with isolated downpours possible. There is low confidence of rainfall accumulations reaching warning amounts over Northland, Auckland, Coromandel, Bay of Plenty, Waikato, Waitomo, Taumarunui and Taupo.

Meanwhile, a weak ridge covers the South Island and southern parts of the North Island, with outbreaks of showers.

On Wednesday and Thursday, a front is expected to affect the lower South Island and there is low confidence of rainfall accumulations reaching warning amounts about the Fiordland Mountains.

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 Saturday, 20-Jan-2018

Issued: 08:05am Saturday, 20-Jan-2018

Afternoon and early evening wind convergences are expected to produce a few showers over eastern parts of Otago, inland South Canterbury, and Hawkes Bay. In these places, there is a low risk of a few thunderstorms. No thunderstorms expected over the remainder of New Zealand.



Valid to Noon Sunday, 21-Jan-2018

Issued: 09:21am Saturday, 20-Jan-2018

No thunderstorms or significant convection expected during this period.



Valid to Midnight Sunday, 21-Jan-2018

Issued: 09:26am Saturday, 20-Jan-2018

Afternoon and early evening wind convergences should produce a few showers over the central North Island and inland parts of the South Island. There is a low risk of a few thunderstorms over Taihape and the ranges of Hawkes Bay, also over inland Marlborough and the Canterbury High Country. No thunderstorms expected over the remainder of New Zealand.



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.