Severe Weather Outlook

Issued: 10:29am Sunday 17 May 2026

Valid Tuesday 19-May-2026

The ridge of high pressure persists across southern and central New Zealand, while an easterly flow covers northern New Zealand.

There is minimal risk of severe weather.

Valid Wednesday 20-May-2026

The high retreats eastwards, with a northeast flow across northern New Zealand. Strong northwesterlies build over the southern South Island ahead of a front approaching from the Tasman Sea late in the day.

There is a low confidence of severe gale northwesterlies for Fiordland, Southland and Stewart Island from evening.

Valid Thursday 21-May-2026

The high to the east extends a weak ridge over central New Zealand, with a northeast flow across northern New Zealand. Strong northwesterlies over the southern South Island ease as a front from the Tasman Sea stalls over the far south.

There is a low confidence of severe gale northwesterlies for Fiordland, Southland, Stewart Island and Clutha in the morning.

Valid Friday 22-May-2026

A weak ridge lies over central New Zealand, with northeasterlies in the north and a front stalled over the far south.

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 Monday, 18-May-2026

Issued: 7:29pm Sunday 17 May 2026

The trough extending east of Northland is expected to move slowly northwards during the afternoon and evening. Throughout the period, there is a low risk of a few thunderstorms about eastern Northland. For the rest of New Zealand, the risk of severe convection or thunderstorms is minimal.



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.