New Zealand’s north-east is in for yet another soaking later this week, with a potential risk of surface flooding and fresh slips in already sodden areas.

MetService is forecasting a low pressure system to move from the Tasman Sea on to 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.

Its latest severe weather outlook found 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.

Image / MetService

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.

An orange heavy rainfall warning was already in place for Gisborne/Tairawhiti, along with the Wairoa District northeast of Nuhaka, over most of today – while a heavy rain watch has been issued for Hawke’s Bay about and south of Te Pohue up to 8pm tonight.

Looking to the next bout later in the week, MetService meteorologist Andrew James said there were still some differences between different weather models, and the first watches were likely to be issued tomorrow morning.

“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.