It may pay to keep an eye on the sky if you're on Great Barrier Island or the northern tip of the Coromandel, with the MetService issuing a severe thunderstorm watch this morning.

A slow-moving low will lie just north of New Zealand today and Wednesday, with associated bands of rain and thunderstorms affecting the northern part of the North Island.

The MetService has issued a severe thunderstorm watch for the outer Hauraki Gulf and Great Barrier Island. A severe weather watch issued on Monday also remain in place on the peninsula. File Photo.

There is a moderate risk of thunderstorms over the outer Hauraki Gulf and Great Barrier Island from this afternoon through into Wednesday morning. A few of these thunderstorms may produce localised downpours of 25-40mm or rain per hour, and hail of 10-20mm diameter.

'Rainfall of this intensity can cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips,” says the MetService.

'Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain. Hail can cause damage to crops, vegetation and light-weight structures.”

A severe weather watch issued on Monday also remains in place for the rest of the Coromandel Peninsula today and Wednesday.

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.

The MetService recommends people visit Civil Defence's Get Ready Get Thru website for information on preparing for and keeping safe during a storm.