The La Nina weather pattern, which brings warmer weather, is the strongest in several decades and will probably continue until autumn, saysthe National Institute for Water and Atmospheric Research.
Three years ago, the La Nina effect caused serious droughts, though the institute is not yet predicting how much rainfall there will be this time.
It expects summer temperatures to be above average in the east of both islands and in the north of the South Island, and very likely to be above average in other districts.
Principal scientist James Renwick says there's also likely to be normal or below normal rainfall in much of the South Island and in the east of the North Island, and no more than normal rainfall over the rest of the county.
Weaker than normal westerly winds are likely.
Dr Renwick says the hole in the ozone layer is smaller than it has been the past few years, but UV levels in this country are high and people need to be particularly aware of the risk of sunburn.