Climatologist Jim Salinger is warning late winter and spring are likely to be colder than usual.
Dr Salinger is president of the Commission for Agricultural Meteorology with the World Met Organisation.
He says there have been rapid changes in ocean and atmospheric conditions in the Pacific, and it is extremely likely El Nino conditions will prevail in the second half of the year.
Dr Salinger says this will bring cold, southwesterly winds to much of New Zealand and conditions will be very dry along the east coast of both islands, from Northland to Canterbury.
He says it will be much wetter than usual in the far south.
Dr Salinger says it is bad news for farmers as cold, dry conditions inhibit grass growth.