Warmer-than-average temperatures, muggy nights and the risk of thunderstorms are possible this weekend as a blast of tropical air sweeps across New Zealand.

In its latest weather update, MetService said temperatures across much of the country will climb above 20C over the next few days, with warm northerly winds drawing humid air south from the tropics.

Meteorologist Alanna Burrows said Bay of Plenty residents heading to Guy Fawkes celebrations on Thursday night should encounter mainly cloudy conditions with light winds and only the chance of isolated showers.

She urged people to check local fire restrictions before lighting outdoor fires, as some parts of the country remained under high or very high fire danger.

The warm weather is expected to continue into Saturday, with overnight temperatures also staying unusually high.

“It’s not just hot daytime temperatures, we are also forecasting warmer-than-usual nights with many places not dropping below the mid-teens,” Burrows said.

“This is because there is a lot of moisture in the air and this slows night-time cooling.”

While many will welcome the taste of summer, unsettled conditions are also developing.

There is a risk of thunderstorms in inland parts of the North Island on Thursday, with the likelihood increasing on Friday and again on Saturday. Periods of rain are also forecast during the next few days.