Severe Weather Outlook

Issued: 10:20am Saturday 20 Sep 2025

Valid Monday 22-Sep-2025

The active front lies slow moving across central parts of the country. Another front moves out of the Tasman Sea and onto the lower South Island.
There is moderate confidence of warning amounts of rain in the Richmond and Bryant Ranges(including the Rai Valley) in the early morning, and moderate confidence for Taranaki Maunga. There is low confidence of warning rain for southern Westland and Fiordland, and for the Tararua Range. There is low confidence that severe northwest gales will affect the Marlborough Sounds, Wellington and southern Wairarapa, in the morning.

Valid Tuesday 23-Sep-2025

The active front over central New Zealand should move slowly onto western parts of the North Island, while a second front moves weakens over the central South Island.
There is low confidence that a warning will be required for heavy rain for parts of Tasman and Nelson Districts, also northern Marlborough, the Tararua Range, Taranaki, Waitomo and parts of the North Island central high country.

Valid Wednesday 24-Sep-2025

The front should drift slowly eastwards over the North Island, bringing a period of northerly rain. There is low confidence of warning amounts of rain from Taranaki to Taupo and Bay of Plenty, northwards to Auckland and Northland.

Valid Thursday 25-Sep-2025

The front, and an associated low, should move away to the east of the North Island. There is low confidence of northerly rain reaching warning amounts over Coromandel Peninsula, Bay of Plenty and northern Gisborne/Tairawhiti. Another front moves onto the South Island, bringing heavy rain to Fiordland and Westland, but this is not expected to approach warning amounts at this stage.

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, 21-Sep-2025

Issued: 7:23pm Saturday 20 Sep 2025

A trough and associated cold air aloft, moves onto the lower South Island later in the day. There is a moderate risk of thunderstorms for Fiordland and Stewart Island in the evening and at night with this trough, and these thunderstorms may bring heavy rain, 5 to 15 mm/h and small hail. A low risk of thunderstorms extends slightly further east and north from the moderate risk. For the rest of New Zealand, the risk of thunderstorms or significant convection 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.