Severe weather warnings have been issued for the upper North Island as the tail-end of a storm which battered South Australia this week gets set to unleash its remaining wrath over the next 24 hours.

Heavy rain, strong winds and thundery conditions have been forecast for the Northland, Auckland, Waikato, Waitomo, Coromandel and Bay of Plenty regions over the next day.

The MetService this afternoon issued severe weather watches for those regions through to 3.11pm tomorrow.

The storm, which this week knocked out power and caused wide-spread flooding in much of South Australia, will have lost most of its punch by the time it reaches New Zealand, but it could still cause localised flooding and heavy downpours.


"It's no longer a storm but it can produce stormy weather," said WeatherWatch head weather analyst Philip Duncan.

"There will be little pockets of severe weather that we will be monitoring in two areas: one is heavy downpours that will be moving into mainly the North Island during Sunday. The other will be isolated thunderstorms that will also be focused around the North Island."

The bulk of the wet weather would be concentrated in the top quarter of the country,, where the was a risk of some localised flooding.

The stormy weather will herald a major shift in the easterly weather patterns the country has been experiencing for the start of spring.

"The air-flow for the first half of October is turning westerly and it's all because of this change coming in tomorrow. So it's not so much severe weather that it's bringing in it's more that it's bringing in a big change to the pattern that we've been seeing."

Farmers and growers would certainly notice the change with the majority of the rain fall moving from the eastern side of the country to the western.

Monday and Tuesday and Wednesday would see similar unsettled weather and Wednesday would see the start of "traditional" spring weather.

"From Wednesday that's absolutely the green light for the usual roaring forties across the entire country - this is nearly half a month late. For the first half of October it's going to be traditional spring weather which is going to mean lots of westerlies, lots of windy days, lots of warmth - lots of Ws."