Severe Weather Outlook

Valid from Monday 01-Mar-2021 to Thursday 04-Mar-2021

Issued: 2:06pm Saturday 27 Feb 2021

A ridge of high pressure moves away to the east on Monday, as a trough approaches from the Tasman Sea, preceded by a moist northeast flow. This trough should cross the country on Tuesday, followed by unsettled showery northwesterlies.

There is low confidence of warning amounts of rain about the ranges of Buller and western Nelson on Monday and Tuesday, and also Mount Taranaki on Tuesday.

For Westland and northern Fiordland there is low confidence of significant heavy rain on Monday, then moderate confidence Tuesday and Wednesday, with low confidence Tuesday and Wednesday for the remainder of Fiordland.

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, 27-Feb-2021

Issued: 8:40am Saturday 27 Feb 2021

Humid conditions over the South Island combined with daytime heating are expected to produce showers in many inland places. There is a generally low risk of thunderstorms over much of the inland South Island this afternoon and evening. For an area in North Canterbury and another around the border between Otago and Southland there is a moderate risk of thunderstorms this afternoon and evening. If these thunderstorms occur they may lead to localised heavy rain with intensities of 15 to 25mm per hour, or possibly more. No other areas of severe convection or thunderstorms are expected.



Valid to Noon Sunday, 28-Feb-2021

Issued: 8:25pm Saturday 27 Feb 2021

No thunderstorms or significant convection expected during this period.



Valid to Midnight Sunday, 28-Feb-2021

Issued: 8:25pm Saturday 27 Feb 2021

During Sunday, humid conditions are expected to continue in many places. This combined with daytime heating should produce showers in many places. There is a low risk of thunderstorms about much of the South Island and parts of Taihape, Whanganui and Manawatu during the afternoon and evening. For parts of Otago and Southland as shown on the chart, there is a moderate risk of thunderstorms during the afternoon and evening, and these thunderstorms may produce localised heavy rain with intensities of 15 to 25mm per hour or possibly more. No thunderstorms or significant convection expected elsewhere in New Zealand 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.