La Nina’s three-year reign is over, and El Nino is expected to hit the region by winter.
The National Institute for Water and Atmospheric Research [Niwa] said in its just-published April to June climate outlook that a period of particularly unsettled weather is possible in mid-April.
“There’s a real chance that El Nino conditions develop in winter, which could lead to drier and cooler weather than recent years,” it said.
Niwa said La Nina ended in March, and neutral conditions are currently occurring.
El Nino means “little boy” in Spanish and is the opposing half of La Nina [“little girl”] in the naturally-occurring global climate cycle known as the El Nino Southern Oscillation [ENSO].
“ENSO influences rainfall, temperature, and wind patterns around the world, including New Zealand,” Niwa said.
It said El Nino and La Nina episodes happen on average every few years and last for up to a year or two.
El Nino is often associated with stronger or more frequent winds from the west in summer, which can promote dryness in eastern areas and more rain in the west.
“In spring and autumn, southwesterly winds are more common,” Niwa said.
During winter, the winds tend to blow more from the south, causing colder temperatures across the country, it said.
However, because of the persistence of warmer-than-average sea temperatures, a colder-than-average Autumn is unlikely.
“More variable circulation and wind patterns will lead to more variable temperatures.”
“Because of this transition, changeability will be a theme in New Zealand’s weather patterns.
“Mixed air flows during autumn could tend southerly around the start of winter, consistent with a developing El Nino.”
Niwa said the weather during the past month may not be a useful indicator of the weather in the month ahead.
Instead, the next three months could feature near-average or above-average temperatures for Wairarapa.
Rainfall is most likely to be near-normal, but a spell of northerly winds could increase the chance of heavy rain by the middle of this month.
Soil moisture and river flows are likely to be normal.
