Heavy rain and severe northwest gales have been forecast for many central and southern areas, said the MetService

An intense front, embedded in a strong and moist northwesterly flow, moves north onto the North Island on Monday.

"It brings heavy rain, mainly to the west of the South Island. Severe northwest gales are likely to affect many South Island areas, and the lower North island," a MetService spokesperson said.

People are advised to keep up to date with the latest forecasts.

A Heavy Rain Watch is in place for 12 hours from 4pm Monday, December 9, to 4am, Tuesday, December 10, for the Bay of Plenty ranges east of Opotiki. 

"Periods of heavy rain, and amounts may approach warning criteria."

A west to northwest flow is forecast to cover the country on Tuesday, with a weakening front over northern New Zealand expected to move away to the east.

"There is moderate confidence of warnable amounts of rain for the ranges of eastern Bay of Plenty early morning," a MetService spokesperson said.

On Wednesday, the northwest flow over the country is due to strengthen over southern New Zealand ahead of a complex trough of low pressure approaching from the Tasman Sea.

The complex trough should be moving east over New Zealand on Thuesday, followed by a strong west to northwest flow.

"There is low confidence for warnable amounts of rain about the Tararua Range and Mount Taranaki/Taranaki Mounga, the Grey and southern Buller Districts, and also about Fiordland and into southern Westland," a MetService spokesperson said.

"Even though an settled northwest flow continues to affect the South Island, there is minimal risk of severe weather."