Severe Thunderstorm Watch

Period: 7hrs from midnight Sat, 31 Aug - 7am Sun, 1 Sep

Area: Northland, Auckland, Waikato, Waitomo, Taumarunui, Taupo, Taranaki, Taihape, Wanganui, Manawatu, Tararua, Kapiti-Horowhenua, Wairarapa, Wellington

Forecast: An active front is forecast to move over the North Island during Sunday morning, with thunderstorms forecast for many North Island regions About central and western parts of the North Island from southern Northland to northern Wellington, there is a risk of some thunderstorms being severe between midnight Saturday and 7:00 am Sunday.

Some of these thunderstorms may generate localised downpours of 25 to 40 mm/h, especially from Waitomo southwards.

Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips. Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.

Some of these thunderstorms may also be squally, and produce damaging wind gusts of 110 km/h or stronger.

Wind gusts of this strength can cause some structural damage, including trees and power lines, and may make driving hazardous.