Warm, but wet is the weather outlook for this week.

The rainy weather is expected to take hold towards the middle of the week with the arrival of the humid, warmer sub-tropical winds.

MetService meteorologist Claire Flynn said this was a "great recipe" for rain around the country.

"Some heavy falls expected and even a chance of thunder."

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The only ones expected to dodge the wet weather were those in the east of the South Island from Canterbury southwards.

Of the main centres today, Auckland was forecast to be the warmest, with a high of 18 degrees expected. Rain wasn't forecast for the city till Wednesday.

Meanwhile in the capital, Wellington was forecast to be slightly cooler, with a high of 15 degrees and a few evening showers today.

Christchurch was a little warmer, with a high of 16 degrees, and high cloud expected to increase before giving way to rain on Wednesday.

A severe weather watch has been issued for Westland and Fiordland with heavy rain expected for the ranges of South Westland and Northern Fiordland today.

MetService said heavy rainfall for a period was expected in the ranges between Franz Josef and Milford Sound from late this morning to Monday evening.

Three-day weather forecast:

Auckland:

• Today: Fine spells, northeasterlies develop

H: 18C L:13C

• Tuesday: Cloudy periods, odd shower possible. Northeast winds

H: 18C L: 15C

• Wednesday: Rain, heavy at times. Strong northerlies easing later.

H: 19C L: 14C

Wellington
• Today: Cloudy periods, few evening showers. Northerlies
• Tuesday: Fine with increasing high cloud. Northerlies
H: 16C L: 14C
• Wednesday: Rain developing, easing later. Northerlies easing
H: 17C L: 13C

Christchurch
• Today: High cloud. Northeasterlies, fresh in the morning
H: 16C L: 9C
• Tuesday: High cloud increasing. Strengthening northeasterlies
H: 17C L: 11C
• Wednesday: High cloud, early light rain. Northeasterlies easing
H: 19C L: 9C