The North Island is in for the wettest summer in 21 years - ending the recent dry spell which broke numerous heat records.

Weather Watch chief analyst Philip Duncan said the La Nina weather pattern which New Zealand was experiencing at the moment would bring heavy rain to the upper North Island.

"There has been all this talk about droughts, but really we have the wrong ingredients for a drought, although arguably we've had the right start to it."

The La Nina weather pattern has been warming oceans in the Pacific and warm oceans guarantee rain, he said.

"We've been experiencing all of the other symptoms of La Nina, except the rain which will be coming soon."

If this summer follows the pattern of the La Nina of 1988-89, the upper North Island and Auckland could expect to see drizzly weather and "pretty heavy rain" by the end of January, he said.

"Put it this way, if we don't have heavy rain by the end of January weather forecasters and scientists need to closely look at how we predict these events, because there's obviously something wrong."

This is good news for Northland farmers who are struggling with the extremely dry conditions.

It has been so dry that some farmers urged Agriculture Minister David Carter to declare a drought after minimal rain in the past two months set new records for low rainfall in many areas.

However, Mr Duncan said farmers would be happy with the weather predicted for summer.

"It looks like there will be an end to their drought early in the new year. But, I would recommend that they still prepare for a drought to be on the safe side," he said.

Last month was unusually hot and dry for parts of Waikato, New Plymouth and Central Otago which experienced their hottest-ever November weather.

One weather station in Cromwell recorded 32.3C, an all-time record for November.

In the Waikato, a reading of 28.1C in Ruakura on November 28 was the highest in the region in 100 years of record-keeping.