Heavy rain is on its way for the northern areas and it's not expected to ease before the weekend, says MetService.

The low pressure system is expected to move slowly across northern New Zealand from Wednesday to Friday.

MetService is predicting a 'prolonged period of wet weather”, especially for Coromandel Peninsula, Bay of Plenty and Tairawhiti/Gisborne.

It has issued heavy rain watches in Northland, North Auckland, Coromandel, Bay of Plenty and Gisborne on Tuesday.

Heavy rain was likely to start in Northland first on Wednesday morning, then head to Gisborne and north Auckland into the afternoon and evening before hitting Coromandel and Bay of Plenty on Thursday.

Heavy rain was likely to start in Northland first on Wednesday morning, then head to Gisborne and north Auckland into the afternoon and evening before hitting Coromandel and Bay of Plenty on Thursday.

The heavy rain watch in Northland is in place from 9am on Wednesday until 6am on Thursday.

Metservice says heavy rain and thunderstorms were likely, with rainfall accumulations to possibly meet the warning criteria – especially in the north and east.

In Tairāwhiti/Gisborne, about and north of Tolaga Bay, there is a heavy rain watch from 2pm Wednesday to 10am on Thursday.

MetService says further heavy rain was likely late Thursday and Friday.

North Auckland, including Great Barrier Island, is under a heavy rain watch from 8pm Wednesday to 8am on Thursday.

There is another for Coromandel and Bay of Plenty, west of Te Puke, from 1am on Thursday to 6pm on Friday.

Heavy rain is likely to reach western Bay of Plenty on Thursday morning.

Heavy rain is also possible in Hawke's Bay on Thursday and Friday, but on Monday MetService only had low confidence of that happening.

Some eastern areas are only getting a day or two to dry out after heavy rain during the weekend.

Tauranga Airport recorded 61mm on Saturday, while Gisborne Airport had 75mm for the two days of the weekend.

It will reach 16 degrees Celsius in Auckland on Tuesday, with isolated showers and fine breaks in-between. The main rain day in the city is expected to be Thursday.

MetService is forecasting rain for Tauranga from Wednesday through to Saturday, with a high of 16 degrees on Tuesday.

It will hit 14 degress in Wellington on Tuesday, with the first sign of rain is expected on Thursday afternoon.

Christchurch is to hit a high of 13 desgrees on Tuesday, expected to be drizzly from late evening Wednesday, into Thursday, then with some rain on Friday.

Michael Daly and Rachel Moore/Stuff