It could be time to peel off some of the winter layers this week as temperatures look set to rise - even topping 20C in some areas.

After the past few chilly and wet weeks it will be welcome news for most, with forecasters predicting warmer northwest winds to sweep the country.

Daytime temperatures in some eastern areas will push into the high teens, while Napier and Hastings could see the mercury pushing over 20C, MetService meteorologist Peter Little said.

WeatherWatch: (July 28) Warmer weather returns


However, the warmer weather is also likely to bring severe wet weather to some parts, with a severe weather warning already in place for parts of the South Island's West Coast overnight and into tomorrow.

Around 90mm of rain is likely in the Westland ranges within 12 hours tonight, and residents are warned to watch out for rapidly rising streams and rivers, and hazardous driving conditions.

"Further bursts of heavy rain are expected to affect the West Coast throughout this week, as several frontal systems embedded in this northwesterly flow cross the country," said Mr Little.

"Fanning those warmer temperatures in the east will be strong to gale northwesterlies. These winds may reach severe gale force in some eastern areas and about the capital later this week, so people should keep up to date with the latest MetService forecasts as warnings and watches may be issued."

A severe weather watch for heavy rain has also been issued for Buller, Westland and Fiordland until Tuesday morning.

Meanwhile, last week had been confirmed as the coldest of the year for many parts of the country, according to MetService.

"Auckland had its coldest week of the year, with a mean temperature of just 8.4C, [which is] 2.5C below average for this time of year," Mr Little said.

"At Kelburn, in Wellington, we had a whole week where the temperature remained in single digits. The Garden City also shivered last week, averaging just 4.6C, which is 1.2C below the July mean."