Weather: Warnings of 'high-impact rainfall', motorists urged to 'stay alert'

Some North Islanders are being told to brace for heavy rain and thunderstorms as a large low settles over the top half of the country.

Wild weather is expected to set in and NIWA principal scientist Chris Brandolino told The AM Show it could be intesnse. MetService on Wednesday morning issued a severe thunderstorm watch for the Coromandel Peninsula, Waikato, Waitomo, Taumarunui, Bay of Plenty, Rotorua, Taupo, Hawke's Bay, Taranaki, and Taihape.

"It'll rain quite hard - it could be a good puff of wind potentially - there could be localised flooding," Brandolino said.

Heavy rain warnings remain in place for Taranaki north of Eltham and Bay of Plenty. 

"The most active area of thunderstorms is forecast for the central North Island, with a high risk in the afternoon and early evening from Waikato and Bay of Plenty to Tongariro National Park," MetService said in its thunderstorm outlook.

"These thunderstorms may produce localised rainfall rates of 10 to 25mm/h and possibly more, strong wind gusts of 80 to 100 km/h, and a slight chance of a small tornado."

NZ Transport Agency Bay of Plenty system manager Rob Campbell is urging motorists to stay alert.

"Avoid unnecessary travel, drive to the conditions, and watch out for surface flooding, slips, and fallen trees or branches," he said.