Weather experts say New Zealand has had a near-record warm summer so far but they warn February could bring heavy rain.

He says most areas are in 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 says.

MetService meterologist Ashlee Parkes says heat alerts were in place today for Taupō, Lower Hutt, Queenstown on Monday, and Napier and Christchurch for Wednesday.

She says there will be little relief overnight for some places with Tuesday and Wednesday expected to be particularly warm and muggy.

However, Noll says some parts of the country can 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 says 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.