Another atmospheric river is set to bring more heavy rain and strong winds across much of New Zealand, with 23 alerts in place before the storm hits today.

Forecasters are warning of two back-to-back weather systems striking in days that threaten to drench Northland, Auckland and the upper South Island.

With areas like Tasman expected to experience a 16-hour deluge, emergency operation centres are already being set up.

This morning, 23 weather warnings and watches were in place across both islands, including 10 orange heavy rain warnings. MetService said there is a “high chance” that warnings over the upper South Island will be upgraded to a severe red warning.

There is also a risk of monster swells of 3 to 4.5m for parts of the coast between the Bay of Islands and Whakatane.

MetService head of weather Heather Keats told Herald NOW’s Ryan Bridge that this morning would be the last of the clear, fine weather for many, with heavy rain and strong winds forecast to sweep in overnight.

“So what people are going to see is an uptick in winds. We’ve got strong nor’easters for places like Northland and Auckland. By late this evening, they’ll be gusting 90km/h.

“And then the rain follows a few hours after with an array of rain watches and warnings in place for the North Island and for the South Island.”

She said the Tasman, Nelson and Marlborough regions remain an area of concern. An orange heavy rain warning is in place.

Tasman council prepares

Tasman District Council said it would be activating its Emergency Operations Centre this evening ahead of the forecast 16-hour deluge.

The council said wind direction would play a big factor in the extent of potential flood threat.

“If the wind does move more to the northeast [instead of northerly], then rainfall is more likely to accumulate in some of those more vulnerable catchments of the Upper Wai-iti and Upper Motueka Rivers.

“Those areas that were damaged previously are being asked to take care. Stock should be moved to higher ground, and extreme caution should be taken around waterways. Slips are possible with this event, especially in the Takaka and Mārahau areas, which are still quite wet.”

The council would pre-emptively close vulnerable roads if conditions worsened.

Keats said the rain will be “quite intense” early tomorrow and the warnings are in place until tomorrow night.

The orange warning meant a potential for surface flooding and slips, particularly for northwest of Tasman.

”And because the wind’s coming from the north, northeast, we know that hammers the region, and it’s when it’s in this vulnerable state.”

Northland would be first to see the strong winds hit from 5pm before moving south. The rain would start falling from 8pm and not let up for 12 hours.

Auckland was expected to see the wind pick up at 10pm and the rain start at 3am and not stop until 10pm on Tuesday.

A heavy rain warning was now in force for Bay of Plenty with up to 180mm rain expected to fall across Tuesday and bringing a threat of flooding and slips.

A similar level of rain was expected to fall in Tasman with 16 hours of rain forecast from 2am tomorrow and lasting until 6pm. MetService said there was once more a threat of rapidly rising rivers and flooding and slips. There was a moderate chance of upgrading to a red warning.

Flooding at Riwaka, on Friday, July 11, when a state of emergency was in place in the Nelson Tasman region.

Nelson Tasman Civil Defence said that although the water table is not as high as in previous weeks, there is still no room for complacency.

“It is, however, still a fair amount of rainfall, so care is needed in exposed areas and those previously affected by the flooding. Land slips are possible.”

Flooding over recent weeks left homes in Nelson, Tasman and Marlborough uninhabitable, roads damaged and properties inundated with flood waters in what was described by local authorities as a “one-in-100-year event”.

Slips, surface flooding and significant damage from the floods have rendered many roads across the upper South Island unsafe.

MetService meteorologist Alwyn Bakker said there was a “high chance” the area’s orange warning would be upgraded to red - the most severe warning.

Additionally, there was the risk of swells of 3 to 4.5m along the coast between Bay of Islands and Whakatane.

“Northeast swell is expected to peak at 4m in the Bay of Islands on Tuesday morning, and at 4-4.5m at Great Mercury Island in the evening. Northerly swell is expected to peak at 4-4.5m at Whakatane around midnight,” Bakker said.

Keats said this weather system would move off the country on Wednesday before being quickly replaced by another.

“There is another low that is set to move over the North Island from Thursday and Friday. So while the watches and warnings are in place at the moment, that’s for this particular system, which is Tuesday, Wednesday, but there’s the chance that this low on Thursday and Friday could bring another level of watches and warnings, including some more impactful weather for Auckland and Northland and Gisborne”

Keats also said temperatures are expected to rise this week, with places like Whangārei only dropping to 15C.