Record-breaking temperatures are expected this month as sub-tropical weather descends on the country.

Today Napier looks set to beat its previous record high for May with a temperature of 27C.

WeatherWatch head weather analyst Philip Duncan said for many parts of New Zealand the average day-time high in May would be in the mid to late teens - this week, temperatures would be in the low to mid 20s.

He said warm spells in autumn were normal, but not as warm or as long as this one - which is believed to potentially extend into the third week of May.


Federated Farmers Hawke's Bay provincial president Will Foley said normally high temperatures in May meant more grass growth, but because the weather had been very dry the expected heat would just "compound the problem".

Farmers had enjoyed a good spring, he said, so they would have some feed on-hand, but others would be holding off getting more stock until there had been enough rain.

"Most farmers thought that with the El Nino predictions that they had dodged a bullet."

He said unfortunately farmers would not be getting away without a dry spell.

"Farmers are gutted," he said. "We had such a good season up until the start of the year and now the weather has come back to bite us."

Hawke's Bay Fruitgrowers Association president Lesley Wilson said most fruits were off, so the high temperatures would not affect fruit quality.

Growers would be keeping an eye on irrigation to make sure trees were well watered going into winter.

Mr Duncan said a high-pressure system was pulling sub-tropical air down over the country, and WeatherWatch believed the warm weather could last until May 10, with "warmer than average weather potentially extending into the third week of May for some areas as windy, warm westerlies continue after the sub-tropical airflow eases".

He said some might call it a "heatwave", while others would say that highs in the low to mid 20s isn't "hot".

"However, either way it's a significant warm spell for May in New Zealand," he said.

As well as the high of 27C, today was expected to be sunny with some high cloud and northwesterlies.

The warm temperatures would continue tomorrow with another 26C high, and a fine day with variable high cloud and northerlies picking up.

Thursday was predicted to have some scattered rain, clearing later.

There would also be northwesterlies in exposed places at first before easing, and a high of 24C.

Friday would be fine with northerlies, which were expected to begin to die out on Saturday, which would be fine with a high of 22C.