Weather experts say New Zealand has had a near-record warm summer so far but they warn February could bring heavy rain.
Niwa meteorologist Ben Noll said the high temperatures were the result of sub-tropical winds, a marine heatwave, and La Niña.
He said most areas werein for a warm few days and nights as a humid tropical system makes it over the country.
"All these things together [are] influenced by the background warming that is climate change, so we've seen more heat extremes and little or no cool temperature extremes so far this summer - of course December was New Zealand's fourth warmest December on record," he said.
Metservice meteorologist Ashlee Parkes said heat alerts were in place today for Taupō, Lower Hutt, Queenstown, and for Wednesday in Napier and Christchurch.
She said there would be little relief overnight for some places, with Tuesday and Wednesday expected to be particularly warm and muggy.
However, Noll said some parts of the country could expect to see very heavy rainfall from the middle of this week.
"It has been a very hot and in some regions dry summer to date but early February the script will be flipped and we're going to have some very heavy rainfall [in] western and northern areas of the South Island in particular."
Noll said the incoming heavy rain could lead to flooding and he urged people holidaying in the South Island to keep an eye on the day-to-day weather forecast.
