"Should little or no rain be reported at the airport by tomorrow at 9am then the record will be broken," Best said.
MetService forecasters are however expecting a southerly change to move through to Christchurch overnight Monday through to early Tuesday, bringing a period of rain to the region.
Rain and showers are in the forecast for most parts of the North Island.
It would be mostly cloudy with a few showers about northern Hawke's Bay and coastal Gisborne, and showers developing into possibly heavy and thundery falls in the afternoon and evening about the central areas.
Nelson and Marlborough can expect scattered rain, clearing and becoming fine in the afternoon.
Elsewhere in the South Island, occasional showers will be clearing in Buller tomorrow while turning to rain with heavy falls in Fiordland, spreading over Westland.
On Tuesday, isolated showers are forecast north of Auckland, and rain or showers for most in the South Island.
Early showers north of Auckland will end the week, and the South Island will be mainly fine except for rain developing in Fiordland and showers further south.
Another Metservice meteorologist, Georgina Griffiths, is predicting the "abnormal warmth" was likely to continue.
"Well above average December temperatures are forecast right across the country," Griffiths said.
"This is helped along by the extremely warm seas surrounding New Zealand."
Below average rainfall is forecast across most of the South Island, and in regions west and south of the North Island.
However, frequent northeasterly wind flows expected during December will bring near-normal rainfall in the north and east of the North Island.
WeatherWatch head analyst Phil Duncan said although a cooler week was coming, for most the weather would still be warmer than average.
"A cooldown is coming, especially for those in the very south and east of both islands, but for many areas the week ahead remains warmer than average or average," he said.
"Inland areas are least likely to feel the cooldown, although on Friday the Central North Island will be cooler and eastern areas even more so."
In the North Island, southerly change would be enough to "knock back humidity levels" even if daytime highs remain two to seven degrees above normal for the first half of December.
Some areas will be more than 8C above normal, especially tomorrow and Tuesday.
"By Wednesday these 'hot spots' will be much more isolated around Hawke's Bay and some of the South Island mountains," Duncan said.
"This 8-plus degrees above normal zone will expand across more centres and regions in the South Island on Friday - while the North Island will be coolest."
