Severe Weather Outlook

Valid from Thursday 04-Jun-2020 to Sunday 07-Jun-2020

Issued: 2:18pm Tuesday 2 Jun 2020

A low over the Tasman Sea approaches New Zealand on Thursday, then crosses the North Island on Friday, followed by a narrow ridge of high pressure. The low should bring a period of rain and strong cold southerlies to much of the country, and snow to some of the South Island mountains and passes.

On Thursday there is low confidence rainfall accumulations will reach warning criteria about northwest Nelson, the Marlborough Sounds, Wellington to Horowhenua but mainly the Tararua Range, and for the central high country from Taranaki and Waitomo across to the eastern ranges of Bay of Plenty, as indicated on the chart.

A cold front is expected to move up the country on Saturday, followed by a new ridge of high pressure. Another period of rain or showers is forecast for many areas on Saturday, and snow may affect some of the South Island passes.

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 Wednesday, 03-Jun-2020

Issued: 7:26pm Tuesday 2 Jun 2020

An active frontal system is expected to move quickly eastwards across the North Island during the afternoon and evening, bringing a brief burst of heavy rain to central and northern areas. There is a moderate risk of thunderstorms over Northland during the afternoon and early evening, and for North Taranaki and the northwest corner of Nelson at night, which may produce localised rainfal rates of 10 to 25mm/hr. A broader low risk area at night extends from Bay of Plenty to Waikato and South Taranaki, also northwest Nelson, as depicted on the chart. No thunderstorms or severe convection 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.