Severe Weather Outlook

Valid from Wednesday 28-Oct-2020 to Saturday 31-Oct-2020

Issued: 2:10pm Monday 26 Oct 2020

A ridge of high pressure covers most of the country on Wednesday and most of Thursday, as the remains of a weak front moves slowly north over the North Island. The ridge moves slowly away east later on Thursday, allowing a series of fronts to pass over the South Island on Friday, then over the North Island on Saturday.

On Friday and Saturday there is moderate confidence of rainfall accumulations reaching warning amounts about Fiordland and Westland south of Otira.

In addition, there is a low risk of severe gale northwesterlies about Fiordland and Southland on Friday, and about Wellington and the Wairarapa on Saturday.

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 Tuesday, 27-Oct-2020

Issued: 7:26pm Monday 26 Oct 2020

No thunderstorms or significant convection expected during this period. Reviewed at 7:25pm Monday - No changes.



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.