Metservice has issued a severe thunderstorm watch for the upper west coast of the North Island tonight.
It says an unstable northwest flow might bring severe thunderstorms, and possibly damaging winds of more than 100 kilometres an hour.
Areas from the west coast of the Waikato, through Hamilton and Auckland, the west coast of the Coromandel and all of Northland should be on watch.
Lightning ⚡️ has increased a bit just off the west coast of the upper North Island (yellow dots).— NIWA Weather (@NiwaWeather) August 12, 2019
Active thunderstorm just north of Dargaville proper. pic.twitter.com/8XKx6rMW0d
It says winds that strong can cause structural damage, affect trees and powerlines, and there is a chance of localised tornados.
The threat period runs until 11pm tonight.