Severe Weather Outlook

Valid from Monday 06-Jul-2020 to Thursday 09-Jul-2020

Issued: 2:27pm Saturday 4 Jul 2020

Unsettled, with strong cold southerlies spreading over the country during Wednesday and Thursday

A broad area of low pressure is expected to cover the South Island on Monday, with a front and northerlies clearing the North Island. The low shifts slowly to the southeast on Tuesday, with embedded troughs and showers passing over the country in the west to southwest flow. A bitterly cold southerly is expected to to move north over the South Island on Wednesday, then the North Island on Thursday, with snow to low levels about the South Island.

On Monday, there is a high confidence that rainfall accumulations will exceed warning amounts about eastern Bay of Plenty and northern Gisborne, with northeast gales about central and western parts of the North Island south of Auckland and north of Manawatu. Watches are currently in force.

Meanwhile, southerlies over the lower South Island bring rain and the moderate risk of warning amounts about southern Fiordland, Southland, Clutha and Dunedin about and south of the Peninsula.

During Wednesday and Thursday, there is a moderate risk of severe gale west to southwesterly winds about Northland, Auckland, and Coromandel Peninsula, with a low risk of severe southerly gales about the east coast of the South Island from Otago through to Marlborough. Cold temperatures are expected, with snow to low levels about eastern and southern parts of the South Island, and about the central plateau of the North Island. There is a low risk that snow accumulations will exceed warning amounts from about 400 metres about southern Fiordland, Southland, Clutha, Dunedin south of Otago Peninsula and Banks Peninsula.

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 Sunday, 05-Jul-2020

Issued: 8:27pm Saturday 4 Jul 2020

Updated at 8:15pm Saturday - Moderate risk confined to northern and eastern parts of Northland and Auckland. A front will continue to lie slow-moving over the southern South Island during the second half of Sunday but no thunderstorms are expected with this front. A second front moving out of the north Tasman Sea will move onto the northern North Island from mid afternoon with a band of heavy rain. A trough with heavy showers and possible thunderstorms follows this front in the evening. There is a moderate risk of thunderstorms associated with both the front and trough over northern and eastern parts of Northland in the afternoon and evening, and about the Hauraki Gulf late evening or at night. A lower risk covers other parts of Northland, Auckland and Coromandel Peninsula in the evening and at night as indicated on the chart. These thunderstorms will be accompanied by heavy rain and strong wind gusts. No other thunderstorms or significant convection expected over 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.