MetService has issued a Severe Thunderstorm Watch for Hawkes Bay. The watch is valid for eight hours from 3pm to 11pm on Saturday January 20.

"This is an alert for the potential of localised downpours for inland parts of Hawke's Bay south of SH 5, and near the coast south of Hastings," says a MetService spokesperson.

"Between 3pm and 11pm tonight, localised downpours of 25-40 mm per hour may affect parts of this area. These downpours could occur with or without thunderstorms."

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.

For information on preparing for and keeping safe during a storm, see the Civil Defence Get Ready website.

Heavy rain on Sunday and Monday

MetService says South Island West Coast rain has eased, but heavy rain is expected for Gisborne/Tairawhiti on Sunday and Monday.

"Heavy rain that has affected the South Island West Coast over the last few days has eased, and all Warnings and Watches there are now lifted," says a MetService spokesperson.

"On Sunday and Monday, an humid east to northeast flow is expected to affect Gisborne/Tairawhiti, bringing a period of heavy rain to the region where a Watch and a Warning are in force."

A Heavy Rain Watch is in place for Gisborne/Tairawhiti south of Tolaga Bay. This is valid for 12 hours from 11pm Sunday January 21 to 11am Monday January 22. 

Monday January 22
A sub-tropical low moves southwards over the northeast of the North Island, and warnings and watches are in place.

Meanwhile, a trough moves onto southern New Zealand from the west.

There is high confidence that rainfall amounts will reach warning criteria about Gisborne/Tairawhiti from Tolaga Bay northwards, and moderate confidence of warnable amounts of rain for the remainder of Gisborne/Tairawhiti and Bay of Plenty from Whakatane eastwards, plus the Westland and Grey Districts.

Also, there is low confidence that easterly winds will reach severe gale about exposed parts of Gisborne/Tairawhiti. Finally, there is low confidence that northeast winds will rise to severe gale about the Chatham Islands.

Tuesday January 23
The sub-tropical low continues to move away to the southeast, with low confidence of severe northeast gales about the Chatham Islands.

Meanwhile, the trough is forecast to move northeastwards over the remainder of the country. Strong or gale south to southwest winds are likely in many places following the trough, along with cooler, showery weather.

There is low confidence that rainfall amounts will reach warning criteria about the Grey and Westland Districts from the glaciers northwards, and Buller.

In addition, there is low confidence that southwest winds will rise to severe gale for a time about coastal parts of Clutha and Dunedin.

Wednesday January 24
The strong south to southwest flow over the country should ease as a ridge of high pressure builds over the South Island.

Thursday January 25
A ridge of high pressure remains over much of the country.