Weather: Heavy rain, 20C night temperatures as hot, moist air flows across Tasman

New Zealand's in for a summer sauna next week as a wave of heat and humidity sets the country simmering.

MetService says the warm, moist air is being dragged north across the Tasman by strong jetstream winds.

"Prepare for overnight temperatures of 15-20C North Island (and possibly near-30C highs in eastern regions)" it posted to Twitter.

It doesn't just mean uncomfortable nights - the northerlies are set to bring several days of wet weather to western and central New Zealand.

"Persistent rain and heavy falls may cause rivers to rise rapidly in the Tararua Ranges (heavy rain warning in place), which are expected to get significant rainfall from Monday through Wednesday," MetService wrote on Facebook.

"Taranaki, Kapiti-Horowhenua, and Nelson regions are also poised for long periods of rain and heavy falls with heavy rain watches already in place from Monday.

"Gale northwest winds are set to affect regions that lie in the shadow of ranges. Strong wind watches are in place for Wellington, Wairarapa, Marlborough, and Canterbury High Country."