KEY POINTS:
The upper North Island is being put through a weather "eggbeater" as a band of heavy rain is trapped from moving quickly across the country by a high that is not going anywhere fast.
Bob McDavitt, the MetService weather ambassador, said the "blocking high", or stationary high-pressure centre, over the Chatham Islands was the main cause of the torrential rains and high winds that caused havoc mainly in Northland yesterday.
He said it meant a small low in the Tasman Sea had not been able to pass over the country as normal. "The low rotates clockwise and the high anticlockwise so it's like an eggbeater and in the middle you get beaten."
Mr McDavitt said the heavy rain band caught in a "river of wind" from the northeast should have moved through Auckland and on to the Coromandel and Kaimai ranges overnight.
The rain could come down at the rate of 30-40mm an hour particularly on high ground. Mr McDavitt said the rain band should pass over the Bay of Plenty and Gisborne later today and then get pushed off to the east.
A trough of low pressure would sit over the whole country and bring unsettled weather for the weekend.
Mr McDavitt downplayed the effect of Cyclone Becky which had brought rainfall of 100mm in 24 hours to New Caledonia as he said it was "not part of the picture yet".
The situation there paled in comparison with the more than 400mm of rain recorded in Kerikeri in the 36 hours in which the storm passed by yesterday, he said.
Dr Jim Salinger of the National Institute of Water and Atmospheric Research agreed that was a huge amount of rain.
"It's nearly half a metre ... probably one of the heaviest downpours in about 10 years."
MetService Weather Warnings
* Bay of Plenty west of about Te Puke: Heaviest falls early this morning could reach 30mm per hour.
* Ranges of eastern Bay of Plenty and Gisborne north of Ruatoria: Rain falling at 30mm an hour until 4pm.
