North Islanders have had a muggy start to the week with humid days and nights but it won't be sticking around for much longer.
The humidity is being fuelled by a warm, tropic-charged air that's washing over the top half of New Zealand, NIWA forecaster Nava Fedaeff explains.
"It's a tropical air mass and if we trace back where it's coming from, it's around New Caledonia," she told The AM Show on Wednesday.
Cooler drier air is on the way, however, and heavy rain warnings are in place throughout the South Island.
"We've got a front that's moving up the North Island today - it moved up the South Island yesterday and continues to this morning," Fedaeff said.
"After that's gone through it washes all of that humidity away.
"Once that front passes through today, tonight's actually going to be a lot cooler for the North Island already."
Wednesday is expected to be a predominantly wet day for Auckland but temperatures will still reach 25C. Thunderstorms may also kick in on Wednesday afternoon.
"If you don't like the mugginess, last night was actually worse than it's going to be tonight," Fedaeff explained.
National forecaster MetService said on Tuesday most parts of New Zealand can expect some wet weather for the rest of this week.
"A low-pressure system has decided to set-up shop for a couple of days in the deep south," MetService meteorologist Tui McInnes said.
"Because of that, we are being graced with some blustery westerlies and widespread wet weather."
WeatherWatch is describing Wednesday's forecast as "unsettled".
"Rain or showers for most North Island regions today as a cold front moves through, the South Island has a bit of wet weather too, clearing about Nelson through to Canterbury this morning."