Heavy rain on way for North Island

Just when summer couldn't get any worse, heavy downpours are forecast to pound central and upper North Island tomorrow.

Afternoon heating and high humidity tomorrow was likely to produce large cloud build-ups during the day, and possibly into Friday, WeatherWatch forecaster Philip Duncan said.

"These afternoon and evening showers may have torrential rainfall rates which can see drains and small creeks turn into raging torrents in a matter of minutes.''

The rain cloud build-up would be isolated, but the central and upper North Island, mostly through Waikato and Northland, was likely to bare the brunt of it.

Met Service has issued a heavy rain warning for the Bay of Plenty and Gisborne areas until midnight tonight.

People in the area should look out for surface flooding a rapidly rising rivers in the area as 25 millimetres of rain could fall per hour in localised places, Met Service warned.

Mr Duncan said settled and drier weather conditions were forecast to move into the South Island and lower North Island on Thursday.

But the weather was far from settled in Auckland this afternoon as a water-spout of swirling air circled Auckland's waterfront.

The mixture of "unstable weather'' over Auckland City caused the air to swirl and pick up water, Mr Duncan said.

While quite sizeable, Mr Duncan said the water-spout looked quite weak.