July bucks trend of wet year for Whanganui with warmer and drier conditions than normal

Weather in Whanganui was warmer and drier than usual for July. Photo / Bevan Conley

The month of July interrupted what has been an abnormally wet year for the Whanganui region thus far.

According to the National Institute of Water and Atmospheric Research (Niwa), Whanganui had a warm and relatively dry July.

Overall, July 2023 was the fourth warmest July on record for the region, with a mean air temperature of 11.2C, 1.5C higher than normal.

The region also had its fourth highest mean minimum air temperature on record for the month of 8C, 1.9C higher than normal.

Niwa climate scientist Gregor Macara said Whanganui also had a below average amount of rain for the month recording 53mm, 73 per cent of what normally falls in July.

This bucked a trend in the region so far this year, with most previous months recording above-normal amounts of rainfall.

The amount of rain for the year was particularly unusual as the previously active La Niña climate driver meant more northeast winds flowed over the country.

“Relatively speaking, the Whanganui region is actually sheltered from those northeasterly winds by regions like Waikato and Bay of Plenty; the rainfall events would impact them before they make it Whanganui,” Macara said.

For above-normal amounts of rain to fall on the region despite these conditions was unusual, he said.

However, it wasn’t clear if the shift to an El Niño climate driver was the cause of the reduced rainfall, as an El Niño had not fully formed yet.

“The indications suggest that those conditions will be established in the coming months so it’s expected an El Niño will develop and be announced but we’re not quite there yet.”

Rather, he said, a large contributing factor to the conditions was the above-average sea surface temperatures around both the North and South islands.

“As we’re an island nation and our climate is maritime, it’s influenced by the sea. Those warmer seas are contributing to the higher air temperatures we’ve been recording,” he said.

Further north in Ruapehu, July brought a large amount of snowfall, leaving skifield operators relieved and state highways closed for multiple days.

Macara said an increase in southwesterly wind flows would have been a contributing factor to the large amounts of snow, but it was only part of the equation.

“It’s all well and good to have more southwesterly winds but you need them to be associated with cold fronts and precipitation as well,” he said.

Ruapehu had been in a good position by receiving these weather events but it hadn’t been the case for some of the ski areas in the South Island which, until recently, had been struggling with a relative lack of snowfall.

“For whatever reason it can often be the case that certain areas in New Zealand might be doing well for snowfall on a given winter and other areas might not.

“It does seem like Ruapehu has been getting the rub of the green so far this winter in terms of getting a lot of those snowfall events compared to the South Island.”

Looking ahead to the next three months, Niwa’s seasonal climate outlook is for above-average temperatures to persist for Whanganui, with rainfall expected to be near-normal for that time period.

Finn Williams is a multimedia journalist for the Whanganui Chronicle. He joined the Chronicle in early 2022 and regularly covers stories about business, events and emergencies. He also enjoys writing opinion columns on whatever interests him.