Forecasters predict a balmy finale to summer

South Island beachgoers can expect a bumper end to summer, but the news is bad for farmers.

Forecasters are predicting light winds, warmer sea temperatures and hotter days until the end of March.

An intensifying La Nina weather pattern will see anticyclones linger to the east of the South Island, dragging warm sub-tropical air southwards.

However, along eastern coasts there will also be days with cool north-easterly winds, when the highest temperatures will be inland.

In its seasonal climate update released yesterday, the National Institute of Water and Atmospheric Research (Niwa) warned the picture would not be so rosy for southern farmers, with below-average soil moisture levels, coupled with lower than normal rainfalls and river flows, especially south of a line from Buller to Marlborough.

Niwa principal climate scientist Dr Jim Salinger said a moderate to strong La Nina was under way across the equatorial and tropical Pacific Ocean, and was expected to persist.

Sea-surface temperatures were likely to be warmer than average, perhaps by as much as a degree, over the next few months.

December sea-surface temperatures had been about half a degree above normal.

"When you get a La Nina you get more easterlies and north-easterlies, so you get some of the warmest water from the north being pushed in," he said.

In the past few days water temperatures along the North Canterbury coast were about 16deg, falling to about 13deg offshore of Dunedin.

- © Fairfax NZ News