Spring may be nearly here but the cold weather is expected to stick around a little longer, a NIWA forecaster says.
Ben Noll told The AM Show the beginning of spring can be a "battleground" as both cold and warm air makes its way to New Zealand.
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"We've got weather coming in from the north, warm air and that gets mixed in with some Antarctic air, so air that comes from the south, and that's what creates weather, temperature gradients, temperature differences."
That means the next few weeks will see a lot of changeable temperatures, oscillating between warm and cold in some places.
"As we go into the second week of the month unsettled again, a low dropping into the north, lots of rain second half of next week.
"Then a bit of a chill will arise probably for the second week of September, so don't put away the woollies just yet...
"We might be past 20 degrees in Canterbury, Christchurch this weekend, but the following weekend and the one after that, maybe not so nice."
NIWA's spring predictions for New Zealand have been disrupted by an upcoming weather event known as "sudden stratospheric warming" (SSW).
During an SSW, the air above the icy continent warms more than 25C above normal and the usual westerly winds in the stratosphere - 30 to 50km above the ground - reverse direction, disrupting the stable status quo.
The vortex of "stormy and freezing weather" surrounding Antarctica weakens, letting cold air from the south to rush north.
Noll told Newshub earlier in the week it's going to cause a bit of trouble, especially if it combines with a low-pressure system also on its way from the Southern Ocean.
"If that happens, the weather around New Zealand could get quite volatile as we go into the second week of September... The beginning of the spring season looks like it's going to be quite rocky."
Newshub.
