Even the sky may be rocking out to the Foo Fighters tonight, with chances of thunderstorms hitting during the concert.

The American rock act is here to play to more than 40,000 fans in South Auckland tonight, with fellow rockers Weezer and Wellington punks Ayn Randy in support.

But MetService meteorologist Brian Mercer is warning concert-goers to "bring a jacket", as the weather could be getting wild tonight.

Gates opened at 4pm, and fans entering Mt Smart Stadium may already be getting wet.

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"As we speak, there's rain over the city," Mercer said.

Heavy rain was expected to sweep over within the next hour or so, but the worst of it was due to clear up by about 9pm.

But fans could still be in for a drenching, with the possibility of thunderstorms hitting at any time throughout the night.

"There could be very, very heavy rain fall with it, there is still quite a likelihood of that," Mercer said.

Such storms normally lasted about 30 minutes to an hour, and there was no good way of predicting when and where they would hit.

"There's quite a, what we would call an unstable air mass."

Winds could get strong too, with an average of 50km/h and possible gusts up to 70 or 80km/h.

"Bring a jacket would the only [advice]. There's not much they can really do," Mercer said.

With any luck, the rain will have cleared enough by the end of the night that concert-goers would have a dry walk home.

Meteorologist Georgina Griffiths earlier said it was unlikely the show will be marred by the kind of brutal weather that sent fans home cold and shivering when Adele performed in the same venue around the same time last year.

The Foos are playing on the back of stellar reviews of their recent Australian shows, with Music Feeds calling it "more than a concert".

"It's an experience, a story about to unfold, and everyone has their own Foos moment they hold dear," the publication wrote.

Recent setlists shows they'll play plenty of hits, including Best of You, Everlong, Monkey Wrench and My Hero, as well as a handful of songs from their recent album, Concrete + Gold.

It will be their 10th visit here. They were last here playing the same venue in 2015.

KEY INFORMATION
TIMINGS: Gates open at 4pm, with Ayn Randy starting at 5.40pm, Weezer at 6.30pm and the Foo Fighters at 8pm.
TRANSPORT: Tickets include free travel on event buses and trains. Check Auckland Transport's website for timings.
RESTRICTIONS: Organisers warn fans to expect wandings and pat downs at the door. They also ask to "leave bags at home". Only those measuring 200mm x 300mm x 200mm will be allowed in.
WEATHER: The concert will go ahead rain or shine. If rain is predicted, bring a poncho or raincoat as umbrellas are not permitted.