Above-average summer predicted for Whanganui, but not before a cold spell

Niwa has predicted an above-average summer for Whanganui. Photo / Bevan Conley

There are high chances Whanganui residents are in store for above-average temperatures this summer.

The National Institute of Water and Atmospheric Research (Niwa) released its seasonal outlook on Tuesday, which showed a 65 per cent chance of above-average temperatures for the Manawatū-Whanganui area.

The outlook also said the amount of rainfall in the region was most likely to be near-normal, with an elevated risk for dry spells.

“But we’ll also have to be mindful of big rain events, especially coming from the north,” Niwa principal scientist Chris Brandolino said.

This could come in big dumps of rain, he added.

“There’s a flow from the east, and that does tend to expose us to sub-tropical lows, high heat and humidity at times.”

Brandolino said the easterly flows were because of the climate driver La Niña.

La Niña refers to the periodic cooling of sea-surface temperatures across the east-central equatorial Pacific, leading to drier and warmer temperatures overall, with notably more extreme cold spells.

However, low-pressure systems may also bring occasional heavy rain from the north, Brandolino said.

“That sort of airflow is coming off the land, not the water. It’s coming down from the ranges.”

He said the warmer-than-average ocean temperatures would also throw more water vapour into the atmosphere.

“Water vapour is basically the fuel for rain, so when it does rain it can rain quite hard.

“These warmer ocean temperatures will also have an upward influence on our air temperatures because we’re an island nation, and our ocean temperatures are really closely aligned with our air temperatures.”

Brandolino said the warmer temperatures didn’t mean there would be no cold periods.

“In fact, the first two weeks of the summer season are beginning on a cool note.

“But those first couple of weeks of December will be the exception and not the rule.”

The Niwa outlook also said soil moisture levels and river flows were most likely to be near-normal over summer in the region.