Severe Weather Outlook

Valid from Wednesday 25-Jul-2018 to Saturday 28-Jul-2018

Issued: 02:12pm Monday, 23-Jul-2018

A disturbed westerly flow covers the country from Wednesday through Saturday. The risk of associated severe weather during the outlook period is minimal.

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, 23-Jul-2018

Issued: 07:36am Monday, 23-Jul-2018

A broad trough, with an associated southerly change, moves slowly across central New Zealand today, bringing scattered heavy showers. There is a low risk of thunderstorms from South Taranaki to Wellington and southern Wairarapa, also the Marlborough Sounds, western Nelson and Buller. There is also a low risk of thunderstorms near the Canterbury coast today, as indicated on the chart. No thunderstorms or severe convection expected elsewhere.



Valid to Noon Tuesday, 24-Jul-2018

Issued: 09:03am Monday, 23-Jul-2018

A broad trough of low pressure lies across the lower North Island, while temperature in the upper atmosphere are cold. There is a low risk of a few thunderstorms from Waitomo to Whanganui, also Wellington and coastal parts of Wairarapa and Marlborough. No thunderstorms or severe convection expected over the remainder of New Zealand.



Valid to Midnight Tuesday, 24-Jul-2018

Issued: 09:06am Monday, 23-Jul-2018

The trough of low pressure lies over lower and central North Island throughout the afternoon and evening, while temperatures in the upper atmosphere remain cold. There is a low risk of a few thunderstorms from Waikato to Whanganui, also Wellington, coastal Wairarapa and the Marlborough Sounds. 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.