New Zealand has seen its warmest September on record, data from the National Institute of Water and Atmospheric Research (NIWA) shows.
The nationwide average temperature was 11.9 degrees, 1.3 degrees above the September average between 1991 and 2020, making it the warmest September since 1909.
Wairoa recorded 29.6 degrees late last month - the highest temperature on record for September in the North Island.
Of the six main centres, Auckland was the warmest.
Meanwhile, NIWA said rainfall was also above normal in parts of Southland, Otago, Canterbury, coastal Wairarapa, Gisborne, Bay of Plenty, Waikato and Auckland - ranging between 120 percent to over 149 percent of normal levels.
But in contrast, rainfall was just 50 percent to 79 percent of normal levels in parts of the Hutt Valley, Kāpiti Coast, Manawatū-Whanganui, southern Hawke's Bay, and Banks Peninsula.
Last Friday, NIWA declared the official arrival of El Niño.
NIWA said the country will see dramatic temperature swings over the next three months, with periods of unseasonable warmth followed by sharp cold southerlies.
Fire and Emergency national wildfire manager Tim Mitchell earlier said there could be a see-sawing of fire danger where New Zealand goes through high and low periods.
"But as we get closer to Christmas and we don't see that rainfall keeping up we think that we're probably going to go into a probably a more drying period and that high fire danger risk."
Now was the time to prepare, he said, clearing vegetation, setting up water supplies, cleaning gutters and forming a plan.