Humidity on Christmas and Boxing Day in Northland could be as high as 30C before a cooler south westerly wind brings relief.
The effects of tropical Cyclone Evan will also be felt in Northland early Monday but more rain than winds are on the cards, WeatherWatch has warned.
After battering Samoa and Fiji in the past week, Evan has been downgraded to a low only but had the potential for heavy rain in places with strong onshore winds.
WeatherWatch head analyst Philip Duncan said the centre of Evan would cross over Northland late Sunday or early Monday with humid northerly wind and rain.
He said the region was on the "edge" of a low that was affecting a small area between the Coromandel and East Coast.
Saturday morning, he said, looked fine but the weather would change once the south east winds picked up later in the day. Mr Duncan said people should not cancel their trips or camping but should be aware of risks and dangers associated with rising rivers and streams.
"However, on Sunday, the centre of the low will change from tracking south to tracking west which is very unusual but that should bring patchy rain," Mr Duncan said.
On Sunday, there is an almost equal chance of it either swinging away from the North Island, into the north Tasman Sea, or heading towards East Cape.
"It is looking increasingly likely that Evan will pass very close to northern parts of New Zealand," he said.