Severe Weather Outlook

Issued: 10:24am Saturday 19 Sep 2026

Valid Monday 21-Sep-2026

A series of fronts are expected to move onto the South Island from the southwest. A ridge of high pressure lies over the North Island.

Strong northwest winds are likely in some South Island areas. Rain is expected in the west and snow may affect some of the higher roads. However, it is unlikely that broadscale warnings will be needed.

Valid Tuesday 22-Sep-2026

A west to southwest flow becomes established over the country as fronts move northeast. Some snow is possible about the higher roads of the northern South Island and central North Island.

For Stewart Island and the south coast of the South Island, there is low confidence that the west to southwest winds will be strong enough to require a warning.

Valid Wednesday 23-Sep-2026

The strong southwest flow over the country is expected to ease slowly as a high over the Tasman Sea moves closer.

There is minimal risk of severe weather.

Valid Thursday 24-Sep-2026

A high over the Tasman Sea slowly moves closer to New Zealand.

There is minimal risk of severe weather.

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 Sunday, 20-Sep-2026

Issued: 7:22am Sunday 20 Sep 2026

An unstable showery southwest flow affects the east of the North Island this morning and afternoon. There is a low risk of a few thunderstorms about parts of eastern Taihape, Hawke's Bay and southern Gisborne/Tairawhiti this morning and early afternoon, as depicted on the chart. There is minimal risk of thunderstorms or significant convection elsewhere during this period.



Valid to Noon Monday, 21-Sep-2026

Issued: 7:42am Sunday 20 Sep 2026

There is minimal risk of thunderstorms or significant convection during this period.



Valid to Midnight Monday, 21-Sep-2026

Issued: 9:02am Sunday 20 Sep 2026

There is minimal risk of thunderstorms or significant convection 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.