Cheat sheet: Atmospheric river brings wet and warm weather from mid week
Wet and warm conditions are expected to arrive in New Zealand from Wednesday after a relatively calm start to the week.
Low pressure over the Tasman is set to draw in a flow of moisture, creating an atmospheric river that will bring heavy rain from the tropics.
Here’s what you need to know.
What is an atmospheric river?
An atmospheric river is a band of moisture flowing through the atmosphere, much like a river, bringing heavy rainfall, MetService meteorologist Samkelo Magwala explained.
It is associated with low-pressure systems and is expected to affect New Zealand from Wednesday to Thursday, starting with the South Island before moving north.
What areas of the country will be the worst affected?
According to Magwala, the worst-affected areas on Wednesday would be in the West Coast of the South Island, including Westland, Grey District, Buller and Nelson regions.
“Rainfall will become heavier in those areas on Thursday, specially in the Nelson region,” he said.
As the weather system moves north later on Thursday into Friday, rainfall will increase in parts of the North Island, particularly the western areas and central parts, including Taupō and the Bay of Plenty.
By Friday, the weather will ease in the South Island, but rain may still linger in some areas, Magwala added.
How are the temperatures looking for the week?
This week will see warmer temperatures, with a shift from dry to wetter weather.
Magwala said that temperatures are expected to rise into the upper teens to low 20s for the North Island, especially as the week progresses from Wednesday into Saturday.
With moist airflow covering the country, overnight temperatures are also expected to be in the mid to high-teens.
According to MetService, Auckland is set to experience night time lows around 18C for most of the week, while Christchurch will see a low of 15C on Friday morning, its warmest overnight temperature in over a month.
“The last time much of the country saw overnight temperatures this warm was mid-February with a similar system from the Tasman Sea,” MetService meteorologist Mmathapelo Makgabutlane said.
“The result will be very different feeling weather compared to the cold fronts from the southwest that have been the norm recently.”
Will this wetter weather continue into next week?
Yes, the wet weather will continue into next week. Magwala said that another system is expected to develop by Sunday, bringing more rain through Monday.
While it won’t be as intense as the current atmospheric river, Magwala added, it will contribute to the ongoing wet conditions.
A brief break in the weather is expected from Tuesday, but the forecast could change as the situation develops.
– Stuff, Sanda Arambepola
March 31, 2025 •07:55pm
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