Napier's turned into a city of vintage umbrellas as thousands arrive for the city's Art Deco Festival.

But those staying for the weekend might just find themselves needing them for cover, with forecast heavy rain a possible dampener for the festivities.

It's warm and fine in Hawke's Bay today, upwards of 30 degrees Celsius, but MetService meteorologist Andy Best said Friday was as good as it would get for the weekend.

Saturday's temperatures will also hit 30C in Napier but a chance of heavy rain and even thunderstorms is present.

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"Clouds will gradually begin to increase on Saturday morning," Best said.

"We expect rain to develop in the afternoon and there is a change that there may be some heavy and thundery falls on Saturday afternoon as well."

Last year's festival attracted around 40,000 people and at popular times there can be more than 20,000 people in the central city, with over 300 events across five days at this year's festival.

Overnight temperatures on Saturday will hit a low of 14C, thanks to a front passing over bringing in a south-west change.

Temperatures will be "much cooler" of Sunday, with a high of 22C and a low of 13C.

"On Sunday, we are looking at some cloudy periods with a few showers," Best said. "The showers are expected to clear throughout the course of the evening however, with southerlies throughout the day."

As the vintage car parades, fashions shows, outdoor concerts, dining experiences and more come to a close on Monday, temperatures will remain lower.

"Monday will be partly cloudy conditions with some light winds," Best said.

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"Temperatures will be around 21 degrees maximum, with a minimum of 13 degrees."