A humid, summertime storm is brewing over the North Island where heavy rain, thunder, lightning and even hail could be on the way for parts of the North Island.

MetService has issued a Severe Thunderstorm Watch from Manawatu to Waikato.

Areas affected include Waikato, Bay of Plenty, Rotorua, Taupo, Gisborne, Hawkes Bay, Taihape, Manawatu and Tararua.

Forecaster Allister Gorman says cloud will start building this afternoon, with the first thunderstorms possible around 3pm.

He says the stormy weather could be very localised though, making it hard to predict exactly where it'll hit.

"Could be quite a bit of lightning in some places and rainfall could be 25 to 40 mm in an hour, which would make driving conditions difficult and can lead to surface flooding or small slips.

"You can be just a few kilometres away and you won't know what's going on. Last week, for example, Palmerston North airport had 40mm of rain in a very short time, in the city they only had 5mm."

Gorman says if the rain does bucket down we could see flash flooding, especially about low-lying areas.