Daytime heating and wind convergence will likely produce a few showers about Bay of Plenty east of Te Puke and the ranges of Gisborne, with a low risk of one or two of these showers developing into thunderstorms.

No thunderstorms or significant convection expected elsewhere in New Zealand today.

Issued: 7:30am Wed, 5 Feb
Valid to midnight Wed, 5 Feb

A northwards moving front brings rain to Fiordland and Westland south of Haast during Thursday morning, with a low risk of embedded thunderstorms.

No thunderstorms or significant convection expected elsewhere during this time.

Issued: 7:28pm Wed, 5 Feb
Valid from midnight Wed, 5 Feb to noon Thu, 6 Feb

During Thursday afternoon and evening, there is a low risk of thunderstorms about northern Fiordland, the Southern Alps, the ranges of Westland, Grey and Buller, and inland Nelson and Marlborough. Isolated showers are also likely about the ranges of the central North Island during the afternoon and evening. Some of these showers may be heavy, but the risk of thunderstorms occurring is considered very low.

No thunderstorms or significant convection expected elsewhere in New Zealand during this period.

Issued: 7:30pm Wed, 5 Feb
Valid from noon Thu, 6 Feb to midnight Thu, 6 Feb

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 25mm/h, or more.
Large hail:
Hailstones 20mm in diameter, or larger.
Strong wind gusts (from thunderstorms):
Gusts of 110km/h (60 knots) or stronger.
Damaging tornadoes:
Fujita F1 – i.e. wind speeds greater than 116km/h (63 knots) or stronger.

Note: some tornadic systems such as funnel clouds, waterspouts and small land-based tornadoes are possible with thunderstorms that may not be classified as severe.

Thunderstorm Risk Levels
The likelihood of thunderstorms occurring is assessed for each area and the following potentials are assigned:

• Low Risk – 11 to 30% chance of thunderstorms occurring in the area.
• Moderate Risk – 31 to 60% chance of thunderstorms occurring in the area.
• High Risk – greater than 60% chance of thunderstorms occurring in the area.