A warm winter is shaping up for the lower North Island as easterly winds and mild ocean temperatures combine for a balmier than usual season.
But Niwa's latest seasonal climate report for June to August has not ruled out cold snaps, southerly storms and frosts for many parts of the country, Niwa forecaster Chris Brandolino said.
On top of a warmer winter Hawke's Bay and Wairarapa could get above average rainfall and higher than usual ocean temperatures while the west coast including Wellington and Kapiti would likely get normal rainfall.
Sea surface temperatures over the next three months are expected to be near average off the west coast and above average to the east.
Last month above normal sea surface temperatures warmed further in the eastern Pacific and persisted around the international dateline.
International guidance indicated El Nino was now the most likely outcome for the next three months, though it was still too early to estimate the strength of the event which would probably arrive between late winter and early spring.
''It's brewing we're just not sure what flavour it will be,'' Brandolino said.
Temperatures were most likely to be above average in the North Island and equally likely to be above average or average in the South Island.
Rainfall totals were equally likely to be near normal or above normal for the east of the North Island and the north of the South Island.
For the rest of the country, rainfall totals are most likely to be in the near-normal range.
Soil moisture levels and river flows would likely be below normal in the north of the North Island and the west of the South Island.
Levels could be above normal in the north and east of the South Island. If the El Nino system developed as expected over the next three months, the country could expect a windy, wet spring and summer in the west, while the east suffers through drought conditions. The last El Nino landed in the summer and spring of 2009/2010 and the system, which usually peaks in December, typically creates cooler more unsettled weather on the west