Summer showed up late, and now it's taking off early for some in the deep south.

WeatherWatch head analyst Philip Duncan delivered the bad news this afternoon.

But some are likely already aware of the cold change.

"A cold change is sweeping up the South Island right now, tumbling temperatures by double digits in 10 minutes.

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"Dunedin soared to 27C today and is now 16C. Some areas further south are even colder, only slightly above double digits."

It's going to get worse.

On Tuesday next week an even colder southerly is expected to move through, with temperatures in both Dunedin and Invercargill expected to reach a wintry high of 12C, Duncan said.

"Welcome to the first signs of autumn".

Southland and Otago were the regions mainly affected, but the cold change was also moving into South Canterbury late this afternoon.

Tomorrow is looking a bit brighter, while it will be cool in Southland temperatures warm up a little in inland Otago, and will reach the low to mid 20s across Canterbury.

Summer hasn't yet abandoned the North Island, with dry weather and temperatures around the mid 20s in the upper half of the island expected over the weekend.

The eastern North Island will be hot this weekend, Gisborne will reach 27C and Napier 28C tomorrow.

Early rain is expected in New Plymouth and Palmerston North tomorrow, but Wellington should be dry. All can expect highs in the low 20s.