Signs of El Nino system detected with some time to go

El Nino looks set to bring dry 'spring-like' conditions to NZ until early next year - but there is no way of knowing the extent of its impact this far out. Photo / Jason Oxenham

A growing El Nino in the Pacific Ocean looks set to bring dry "spring-like" conditions to New Zealand until early next year - but there is no way of knowing the extent of its impact this far out, forecasters say.

WeatherWatch head analyst Philip Duncan said meteorologists were starting to see evidence of the El Nino weather system globally.

Soil moisture readings in New Zealand show plenty of rain falling in the west and a dry pattern in the east - a sign of the westerly flow that El Nino encourages.

But people need to be "careful" when talking about its effects, he said.

"I don't support the promotion of dramatic language like, 'This will be the worst drought since the 90s,' as we simply can't know that.

"The long-range forecasts are helpful but they are not the answer as to what is going to happen," Mr Duncan said.

The concern with El Nino was that it would add to what was an already dry and windy pattern for New Zealand, he said.

Mr Duncan said the country's mountainous terrain could also make El Nino weather patterns harsh sometimes.

An El Nino would mean cooler sea temperatures and more highs in the Tasman Sea, fuelling "spring-like" weather over the country - a possible problem for dry eastern areas such as north Canterbury.

" ... time is running out for solid rains in these dry areas," Mr Duncan said.

Australia's Bureau of Meteorology said: "All international climate models indicate El Nino is likely to strengthen, and is expected to persist into early 2016."

What is El Nino?

• El Nino is a climate pattern associated with unusually warm ocean waters in parts of the Pacific Ocean.

• An El Nino event can have a significant impact on weather patterns, ocean conditions and fisheries across a large part of the earth.

• During El Nino, cyclone conditions in the tropical South Pacific shift eastwards, causing more cyclones than normal in areas like the Cook Islands and French Polynesia.

• El Nino can also cause heavy rainfall and flooding over Peru, and droughts over Indonesia and Australia.

• In New Zealand, an El Nino event this year could cause drier "spring-like" conditions.

• El Nino means "The Little Boy" or "Christ Child" in Spanish. It was first observed in the 1600s by fishermen off the South American coast.

Sources: Niwa, WeatherWatch, US National Ocean and Atmospheric Administration.