Lower North Island to experience mixed weather in July; possible heavy rain

Niwa says La Niña could cause a tropical moisture plume in mid-July, resulting in heavy rain. Photo / Bevan Conley

The lower North Island could experience some heavy rainfall this month, according to Niwa’s July-to-September climate outlook.

The rain would be a result of La Niña, a weather pattern known for its colder ocean temperatures, possibly causing a tropical moisture plume in mid-July.

“This represents a wetter trend compared to last month’s outlook, owing to La Niña-like tendencies in the atmosphere,” Niwa’s report said.

Niwa principal scientist of forecasting and media Chris Brandolino said the Taranaki, Whanganui, Horowhenua, Manawatū and Kāpiti regions would experience two different themes over July.

“It will be chilly over the next 10 days, especially overnight and in the mornings coming into the school holidays, and the Lower North Island location may also have some dry weather. As for the next half of the month, those warmer, moist temperatures start, which leads to rain events. This is due to the fact the airflow will become more north or northwesterly.”

He said there may be the potential for early-season warm spells in August and September.

“It’s how things are shaping up in terms of the airflow. We could see high pressure more frequently in the Lower North Island, which would lead to that dry lean.”

In terms of temperatures, there was a 50% chance they would be above average and a 45% chance of near average.

“Temperatures are about equally likely to be near average or above average in all regions of the country. Cold snaps, like what’s expected in early July, will occur occasionally but likely won’t define the season.

“There are expected to be fewer southerly winds, resulting in a reduced risk of frost. July is expected to feature mixed air flows, including a potential spell of moist, northerly quarter winds in the mid-month. During August and/or September, high pressure may become more common near the North Island, seeing a possible return to westerlies,” the report said.

Soil moisture levels were equally likely to be near normal or below normal (45% chance each) while river flows had a 50% chance of being near normal.