Bad news for those hoping the scorching summery weather will last at least until after the U2 concert and Black Caps cricket this weekend.

Cold and rain is expected to put an end to the balmy weather most of the country has been enjoying all week.

Winds have been forecast to pick up, as a warm and moist north to northwest flow covers much of the country through to Saturday, followed by a trough and then a south to southwest change by Monday, bringing cold and rain.

The South Island is expected to be hit first before the front moves slowly northwards tomorrow, MetService said, and this will be followed by a second front moving into the South Island from the southwest.

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"The fronts are expected to bring an extended period of heavy northerly rain to Westland, Buller and the headwaters of the Canterbury lakes and rivers," MetService said.

Auckland, which has had sunny skies and highs of 22-23C all week, can expect showers and rain on both Saturday and Sunday and overnight lows dropping to 12-13C.

Weather in the capital will also worsen from tomorrow, starting with a cloudy Friday followed by showers and rain at the weekend, with highs of 19C but dropping to 16C by Monday.

Christchurch starts the weekend with mainly fine days with highs of 27C, but will be hit by rain by Sunday, taking overnight lows from 16C to 9C.