Weather forecasters think the country is trending towards La Niña conditions this summer.
Photo: NIWA
The National Institute of Water and Atmospheric Research has made its predictions for the next three months.
La Niña is a phase of a global climate cycle known as the El Niño Southern Oscillation, or ENSO for short.
The other phase of ENSO is El Niño. The two phases happen on average every few years and last about a year, NIWA says.
In New Zealand northeasterly winds tend to become more common during La Niña events, bringing moist, rainy conditions to northeastern areas of the North Island and reduced rainfall to the lower and western South Island.
Warmer than average air and sea temperatures can occur around New Zealand during La Niña.
In addition, NIWA is expecting northeasterly winds, moist rainy conditions in the north and east of the North Island and reduced rainfall for the lower and western South Island.
Above average temperatures are expected across all Aotearoa New Zealand, with November being especially warm - especially after the second week of the month.
Unusually warm coastal sea surface temperatures are also forecast - with the potential to cause a marine heatwave in some areas.
Higher than normal air pressure is favoured over the South Island and to the south and east of the country, causing more easterly quarter winds and increasing the chance for dry spells in the South Island and western North Island in particular.
The risk of Pacific tropical cyclones - with heavy rain and flooding - will be higher than normal this summer in the northernmost parts of the country, NIWA says.
"Those with marine interests north of the country should closely monitor the situation," it said.
How La Niña works
"During a La Niña event, ocean water from off the coast of South America to the central tropical Pacific cools to below average temperatures. This cooling occurs because of stronger than normal easterly trade winds, which churns cooler, deeper sea water up to the ocean's surface," NIWA says
"Sea temperatures can warm above average in the far western Pacific when this happens. The unusually cool water in the eastern Pacific influences the Walker Circulation and suppresses cloud, rain, and thunderstorms. This change impacts weather patterns around the world."
