A polar jet stream will make its chilly presence felt this weekend and again next week, bringing with it below-average temperatures as southerly winds hit the country.
A wind chill across most of Aotearoa on Sunday is set to see temperatures plummeting, NIWA warns, which may be reinforced towards the middle of next week.
Southerly winds and chilly temperatures will sweep in as the rain that's been battering the North Island moves east, but Sunday is the day you'll really want to rug up, NIWA says.
"The cold snap will be felt over the country," MetService meteorologist David Miller said.
The far south will see "fairly windy" conditions from Saturday, with wet weather potentially turning into snowfall, he added.
However, the meteorological service noted there are signs the polar jet could become less active heading into June, which may spell milder temperatures.
"This may sound a bit counterintuitive - however, with El Niño ending, its influence on the jet stream patterns is expected to wane," it said.
"Winter may well feature more westerly or northwesterly winds than normal, a stark contrast to autumn's chilly southwesterlies."
As the winds become more southwesterly, cold air will make its way up the country on Friday night and into the weekend, MetService meteorologist John Law explained in his forecast.
Meanwhile on Thursday, a low-pressure system will pull away towards the east, feeding heavy rainfall into eastern parts of the North Island during the morning and possibly into the evening, Law explained.
"As the winds turn a little bit more southeasterly, feeding that rain in towards places like the Wairoa District, up in towards Mahia, and up towards Gisborne/Tairawhiti as well... We still have some severe weather warnings through there.
"We could find some thunderstorms just clipping that coast as well."
Warnings have been downgraded for the likes of the Wairarapa and southern Hawke's Bay, although heavy rain is still possible. The worst is likely to be seen north of the State Highway 5 area, Law said.
As of 7:30am on Thursday, an orange-level heavy rain warning is in place for Hawke's Bay, about and north of SH5. This warning will remain active until 8pm, with the next update at 10am.
Between 50 to 80mm of rain is expected on top of what has already fallen, with the largest accumulations likely around ranges. Heavy rain may cause streams and rivers to rise rapidly, while surface flooding and slips are also possible and driving conditions may be hazardous.
A heavy rain watch is also active for Gisborne/Tairawhiti until 8pm, with periods of heavy rain forecast. Amounts may approach warning criteria, mainly south of Ruatoria.
"By far and away, the wettest weather will be on the eastern coast," Law said.
Auckland and Northland may also see some showers but milder temperatures on Thursday, while lower areas of the South Island could be in for clearer skies but colder conditions - spelling a chilly start to the day. Meanwhile, Wellington may see cooler temperatures on Thursday but drier weather.
