A severe thunderstorm watch is being issued for the Bay of Plenty, Coromandel and Waikato.

The watch is valid for the six hours from 2pm to 8pm today, says the latest update from the MetService.

"Thunderstorms are expected to develop about northern regions of the North Island this afternoon and continue into the evening, producing heavy rain and hail.

"However, in areas of Auckland, Waikato, Coromandel Peninsula, and Bay of Plenty west of Rotorua, there is a moderate risk that some of the thunderstorms could become severe, producing localised downpours of 25 to 45 mm/h.

"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."

A severe thunderstorm watch means conditions are favourable for severe thunderstorms in and close to the watch area.

People in these areas should be on the lookout for threatening weather conditions and monitor for possible severe thunderstorm warnings, says the MetService.