Temperatures are about to lift up across New Zealand with next week much warmer than it usually is in mid-April.

The reason? A large high pressure zone which will be parked east of NZ encouraging a sub-tropical airflow from around Tonga to drift down across the country for a number of days.

"It's not too often in mid-April you're seeing daytime highs in the 20s and/or overnight lows in double digits for basically a week, especially in the lower South Island," says WeatherWatch.co.nz head forecaster Philip Duncan.

Next week looks frost free across the country due to the warm airflows.

"But as we said in our ClimateWatch update for April, the forecast this month was that of 'chaos”. Big highs and big lows helping to produce all sorts of weather from all directions.

"While next week looks warmer than average by day and night across almost all of New Zealand thanks to the sub-tropical airflows, the following week (the last one of April) looks the opposite with westerlies and sou'westers dominating from out of the Southern Ocean and bringing snow back to the southern mountains and overnight lows back to where they should be. In fact, the lower and western South Island looks to be colder than average in April's last week.

"Classic Autumn ups and downs!"