The start of winter could be unseasonably warm, forecasters say.
Between May and July, Niwa predicted temperatures were likely to be above average across the country although cold snaps and frosts were likely to occur, particularly in colder locations, as the season progressed.
Forecasters said the marine heatwave conditions which continued in the Tasman Sea last month meant warmer than normal seas which could lead to shorter and less severe cold spells during the start of winter, according to Niwa's Seasonal Climate Outlook.
Sea surface temperatures around the country ranged from 0.8C to 2.1C warmer than normal.
And the warm seas were likely to continue through the coming quarter, Niwa predicted.