The National Institute of Weather and Atmospheric Research (NIWA) says La Nina will likely bring warmer than average temperatures to New Zealand this summer.
Principal Scientist Chris Brandolino told TVNZ 1's Breakfast programme that the North Island especially will experience warm, humid weather this summer with more tropical airflows reaching the island.
"We think with high confidence that this summer across New Zealand will be warmer than average," Mr Brandolino said.
However, the upper North Island in particular will receive more rain than usual, including Bay of Plenty, Auckland and Northland.
There is also an above-average chance of ex-tropical cyclones reaching New Zealand, Mr Brandolino said.
Some areas, however, are likely to receive less rainfall than average, including the western and southern areas of the South Island - Milford Sound, Southland, Queenstown and Greymouth.
Water temperatures around the country are already above average, he said.
Today marks the first day of the meteorological summer, with several days of heavy rainfall and thunderstorms seeing out the end of spring this week.
The storms are due to continue today, with MetService saying thunderstorms are likely from this afternoon about most of the North Island, as well as parts of the South.
Along with the thunderstorms, hail is possible, in some places severe around the centre of the North Island and upper South Island.
Temperatures today are expected to be warm, with a high of up to 27 degrees Celsius forecast in Masterton - among the nation's highest temperatures - and a high of 29 degrees forecast for five days from now.
For a full forecast, see our weather section here .
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