Severe Weather Outlook

Valid from Saturday 25-Jan-2020 to Tuesday 28-Jan-2020

Issued: 1:38pm Thursday 23 Jan 2020

A front is expected to move up the west of South Island Friday night and Saturday, bringing a brief burst of heavy rain. There is LOW confidence that rainfall accumulations will meet warning criteria in Fiordland and Westland.

A ridge of high pressure should follow later on Saturday, moving northwards on Sunday, with mostly settled weather over the country.

On Monday and Tuesday, however, another front is likely to bring further heavy rain, and there is again LOW confidence of significant accumulations over Fiordland and Westland.

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 Friday, 24-Jan-2020

Issued: 7:54am Friday 24 Jan 2020

A front is expected to approach the far south of the South Island tonight, bringing rain to Fiordland. There is a low risk of elevated thunderstorms developing about central and southern Fiordland tonight. Elsewhere, no thunderstorms or significant convection is expected.



Valid to Noon Saturday, 25-Jan-2020

Issued: 10:28am Friday 24 Jan 2020

The front moves onto the lower South Island during Saturday morning, bringing rain to southern areas, especially in the west. There is a low risk of elevated thunderstorms about Fiordland and southern Westland as indicated on the chart. Elsewhere, no thunderstorms or significant convection is expected.



Valid to Midnight Saturday, 25-Jan-2020

Issued: 11:00am Friday 24 Jan 2020

The front moves slowly northwards onto central parts of the South Island during the second half of Saturday, weakening as it does so. There is a low risk of elevated thunderstorms for southern Westland during Saturday afternoon. In the east, moisture convergences set up along eastern parts of South Canterbury and Otago behind the front during Saturday afternoon and evening and are likely to produce cloud build ups and showers. There is a low risk of thunderstorms for central Otago, Dunedin, North Otago and the far south of Canterbury High Country and coast and plains as indicated on the chart. The thunderstorm risk increases to moderate for the far south of Canterbury High Country, eastern parts of Central Otago and inland North Otago and Dunedin, and any thunderstorms that do develop will be accompanied by localised heavy rain of 10 to 20 mm/hr. Elsewhere, no thunderstorms or significant convection is expected.



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.