Chance of El Nino weather doubles

El Nino can result in greater rainfall in some areas, but also leads to drought in areas that are usually dry. File photo / Duncan Brown

He's a small boy packing a big punch, and Kiwis have been warned to watch out for him this year.

Conditions were ripe for development of the notorious El Nino, MetService said today.

El Nino - usually translated from Spanish as "The Christ child" or "male child" - influenced weather patterns worldwide.

Previous incarnations caused a cocktail of bizarre or unseasonal conditions from droughts to floods in afflicted areas.

It remained unclear how big El Nino's influence would be this autumn, and Federated Farmers said it was wise to prepare for a possible El Nino, but not to panic.

MetService meteorologist Georgina Griffiths said the chances of El Nino manifesting this year were twice as high as usual.

Typically, El Nino brought more rain to western parts of New Zealand, and drier than usual conditions to the east.

Ms Griffiths said today's announcement was meant as a "heads-up" for farmers, who could also expect a colder than usual spring if El Nino developed.

Cyclone Pam, which earlier this month wreaked havoc in Melanesia and the North Island's east coast, had another nasty sting in its tail.

"Cyclone Pam produced one of the strongest reversals of the tropical trade winds seen in recent years. Known as 'westerly wind bursts', these can kick-start El Nino, since they allow warmer waters to push towards South America," Ms Griffiths said.

She said unusually powerful westerly winds would hit New Zealand's west coast if El Nino developed.

But El Nino would not be the biggest influence on weather in April, Ms Griffiths said.

"In the short-term, weather sequences, rather than El Nino, will influence New Zealand rainfall and temperature," she said.

This April was expected to be warmer than average for most of the country. MetService predicted the north and west of the South Island, and southwestern North Island from Taranaki to Wellington would be wetter than normal.

MetService expected typical rainfall in April for the rest of the North Island, Southland, and the South Island's east coast.

Federated Farmers adverse events spokeswoman Katie Milne said farmers in drought-afflicted parts of Marlborough, Canterbury and Otago were most in need of rain right now.

However, Ms Milne said a sudden heavy downpour after a long dry spell was not ideal either, as it could wash away nutrients and ruin soils. Instead, persistent light to moderate rain was needed.

Parasites would "multiply like crazy" and take advantage of sudden surge in moisture after a dry spell.

She advised lifestyle block owners and residents to drench their pets or stock to rid them of parasites when this happened.

Ms Milne said El Nino forecasts were based on modelling that wasn't always accurate and the event was not a foregone conclusion.