Severe Weather Outlook

Valid from Tuesday 11-Aug-2020 to Friday 14-Aug-2020

Issued: 2:17pm Sunday 9 Aug 2020

A complex low pressure system over the Tasman Sea is forecast to move onto the North Island from overnight Monday to Tuesday while a weak ridge lies over the South Island. The low should move east across the North Island on Wednesday. The ridge over the South Island gradually extends north across the North Island on Thursday while a weak cold front moves north over the South Island. It is followed by another ridge on Friday.

On Tuesday, there is high confidence of rainfall accumulations reaching warning criteria in Northland, while the confidence is moderate for Auckland including Great Barrier Island and Coromandel Peninsula.

There is also moderate confidence of warning amounts of rain in Bay of Plenty and eastern Waikato near the Kaimai Range during Tuesday and early Wednesday. From late Tuesday to Wednesday, there is low confidence of rainfall amounts reaching warning criteria in Gisborne and Hawkes Bay, but the confidence increases to moderate about Wairoa District.

Additionally, there is low confidence of of northeasterlies rising to severe gale in exposed parts of Northland, Auckland including the Great Barrier Island and Coromandel Peninsula during Tuesday.

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 Monday, 10-Aug-2020

Issued: 7:27am Monday 10 Aug 2020

No thunderstorms or significant convection expected during this period.



Valid to Noon Tuesday, 11-Aug-2020

Issued: 8:52am Monday 10 Aug 2020

A front is expected to move onto Northland during the morning, bringing heavy rain and northeast gales as detailed in the SEVERE WEATHER WARNING and WATCH. There is a low risk of embedded thunderstorms with this front. No thunderstorms or severe convection expected over the remainder of New Zealand.



Valid to Midnight Tuesday, 11-Aug-2020

Issued: 8:57am Monday 10 Aug 2020

The front should move across northern and northeastern parts of the North Island during the afternoon and evening, bringing a burst of heavy rain and northeast gales as detailed in the SEVERE WEATHER WARNING and WATCH. There is a low risk of embedded thunderstorms with this front for Northland in the afternoon, Auckland and Coromandel Peninsula in the afternoon and early evening, and for Bay of Plenty and the far north of Gisborne at night. A few heavy showers are likely behind this front for Northland, with a low risk of thunderstorms persisting there. No thunderstorms or severe convection expected for 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.