Autumn is well under way with a cloudier start to the day for most of the country, but some areas in the South Island are set to be hit by sweltering temperatures later this week.

Temperatures in Otago, Canterbury and Marlborough would surge up to 30C on Thursday, WeatherWatch meteorologist Philip Duncan said.

"It will be especially hot when the sun comes out," Mr Duncan said.

However, there would be a cool change on Friday with temperatures tumbling more than 10C during the day.

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This would only last until Saturday morning as the high pressure comes in from Tasmania, bringing a settled weekend, Mr Duncan said.

Mr Duncan said it was "quite normal" for temperatures to rise up to 30C in the South Island in March.

"It's all signs of autumn with wild swings in temperatures in the South Island," he said.

Aucklanders would wake up to a cloudy morning most of this week but the nights would be humid.

"There will be some restless sleeps for Aucklanders for the next few days ," he said.

High pressures for most of the main centres this week meant it would be mostly dry and settled.

Wellington is expected to reach 26C today but showers would develop tomorrow, Metservice said.

Showers are also expected on Thursday and Friday.

Hamilton would be cloudy tomorrow with a high of 26C but showers are expected on Thursday and Friday.

Forecast

Auckland:

• Tuesday: Cloudy periods. Southwesterlies. 25C.

• Wednesday: A few morning showers, then fine spells. Southwest eases. 24C.

Hamilton:
• Tuesday: Cloudy periods. Southwesterlies. 26C.
• Wednesday: A few morning showers, then fine spells. Light southwest. 25C.

Tauranga:
• Tuesday: Fine, morning and evening cloud. Southwesterlies. 27C.
• Wednesday: Fine spells, chance afternoon/evening shower. SW dies. 26C.

Wellington:
• Tuesday: Showers develop afternoon, ease evening. Southerly change. 24C.
• Wednesday: Cloudy periods. Strong northerlies developing. 20C.

Christchurch:
• Tuesday: Cloudy periods, a few showers. Southerly change. 23C.
• Wednesday: Morning cloud, chance shower, then fine. N'ly develops. 20C.

Dunedin:
• Tuesday: Cloudy periods, few showers. Strong southwest eases. 18C.
• Wednesday: Cloudy periods, chance morning shower. N'ly develops. 20C.