Heavy rain warnings have been issued for northern parts of the North Island, as nasty weather bears down the country.

MetService has this morning issued new severe weather warnings, saying a low-pressure system is expected to move slowly across northern New Zealand from Wednesday through to Friday.

It will direct moist northeast winds with several embedded fronts across the upper North Island.

“Periods of heavy rain and possible thunderstorms are forecast from Northland to northern Auckland, and southwards to western Bay of Plenty and northern Gisborne, affecting areas that are already saturated from recent rain events. Heavy rain watches are now in force.

“People are advised to keep up to date with the latest forecasts in case further areas are added or upgraded.”

It follows warnings yesterday that the country’s northeast is in for yet another soaking later this week, with a major rain-maker set to bring a renewed threat of surface flooding and fresh slips in already sodden areas.

Today’s alert says a heavy rain watch is in force for Northland between 9am Wednesday and 6am Thursday, with periods of heavy rain and thunderstorms, with rainfall accumulations potentially approaching warning criteria, especially in the north and east.

Similar warnings are in place for North Auckland and Great Barrier Island between 8pm Wednesday and 8am Thursday.

Coromandel Peninsular and Bay of Plenty west of Te Puke also have heavy rain watches in place from 1am Thursday to 6pm Friday, with heavy rain in western Bay of Plenty likely to start Thursday morning.

A heavy rain watch is in place for Tairawhiti/Gisborne and north of Tolaga Bay from 2pm Wednesday to 10am Thursday, with further heavy rain likely late Thursday and Friday.

MetServices rain radar as of 9.50am Tuesday. Image / MetService

Yesterday, MetService warned that a low-pressure system would move from the Tasman Sea onto northern New Zealand on Thursday or Friday, bringing a “prolonged period” of wet weather for northern and eastern regions – particularly Coromandel, the Bay of Plenty and Tairawhiti/Gisborne.

It said there was “moderate” confidence – or a roughly 40 per cent likelihood – that rainfall levels would warrant warnings in Northland on Wednesday and Thursday, Coromandel and Bay of Plenty from Whakatāne westward from Thursday to Saturday.

There was also a moderate chance of warning-level rainfall in Tairawhiti/Gisborne from Wednesday to Saturday – but low confidence of heavy rain for Hawke’s Bay on Thursday and Friday.

MetService also flagged the potential for surface flooding and slips which, after several days of rainfall, could occur regardless of whether warnable amounts of rainfall eventuated.

Parts of Tairāwhiti/Gisborne recorded over 60mm of rain in the 24 hours from 10am on Sunday, and Gisborne itself saw about 30mm in that period. Further south, a few locations in Hawke’s Bay and the Wairarapa also saw about 30mm.

Today is expected to bring a reprieve as the rain eases off, with showers possible in other areas.

Looking to the next bout later in the week, MetService meteorologist Andrew James said there were still some differences between different weather models.

“The message I’d like Kiwis in that part of the country to hear is that, first of all, it’s been a hard run for you guys and we’re thinking of you,” he said.

“The second thing would be to stay up to date with the forecast because anywhere in those areas are in line for some heavier rain, from later in this week to the early part of the weekend.”

James said a “stubborn” high-pressure system remained to the east of New Zealand and was keeping rain-making systems from moving over us quickly.

The high was also helping to drag down warm, moist air from the north – where this year’s relentless run of subtropical “atmospheric rivers” have been sourced from.

Niwa Weather forecaster Ben Noll said that high was “probably the most important player” influencing New Zealand’s current weather.

“It’s like an atmospheric stop-sign that’s blocking the incoming sequence of lows this week from moving away with any real pace,” he said.

“So, you’re locking in this unsettled weather over these regions for extended periods of time, and if you have slow-moving, heavy, convective showers or thunderstorms, then this is just where we’ve run into problems over the last six to 12 months.”

Noll said these La Niña-like patterns also owed to the fact the tropical West Pacific was still running warm – even as meteorological agencies have just declared the start of El Niño.

“So, we’re still seeing the connection to that with plumes of moisture extending down here from the subtropics, and, in some cases, even the tropics.”

Fortunately, Niwa was predicting the pattern would change over July and August – and its seasonal outlook indicated equal odds for normal to below normal rainfall for the northern North Island over the season as a whole.