We've just sweated through our warmest start to a year on record

Wednesday, 4 April 2018

January to March temperature anomalies for New Zealand's three hottest starts to the calendar year on record.

New Zealand has just clocked up with its warmest start to the calendar year on record.

The average temperature across the whole country was 1.75 degrees Celsius above the 1981-2010 average for January to March combined, according to Niwa's March climate summary..

Previously, the record was held by the start of 1999, when the January-March mean temperature was 1.51C above average.

It follows on from our hottest summer on record, the world's second-warmest year on record in 2017 and New Zealand's warmest year on record in 2016.

* It was officially New Zealand's hottest summer on record

* The extremes of the hottest New Zealand summer on record**

March itself was 1.3C above average. That fits with Niwa's autumn climate summary, which said the country would be warmer than normal from March to May.

The marine heatwave experienced in the Tasman Sea played a major role in the warm temperatures.

Niwa said the heatwave was also present in other years with warm starts - 1998, 1999 and 2016.

The marine heatwave was in turn driven by La Niña conditions and higher than usual surface air pressure during summer.

WHAT HAPPENED DURING MARCH

During March, all regions of the country experienced well above average (more than 1.20C of average) or above average (more than 0.51 to 1.20C of average) mean temperatures.

Only isolated parts of Tasman and Southland experienced near average temperatures (-0.50 to 0.50C).

The number of record and near-record high mean minimum night time temperatures in March exceeded the number of record and near-record high mean maximum day time temperatures, Niwa said.

New Zealand’s regional climate over April – June 2018 is expected to be driven by persistence of more northeasterly airflow than normal, and by the persistence of warm ocean waters that are present around the country.

That was due to the marine heat wave and warm and humid northeasterlies keeping overnight temperatures elevated.

March had significantly higher pressure than normal to the east of New Zealand.

That, combined with a decaying La Niña in the tropical Pacific, caused more northeasterly winds than usual over the country.

Those warm, humid air masses, combined with the remnants of the marine heatwave in the Tasman Sea, influenced higher than usual temperatures over New Zealand as well as some heavy rainfall events.

The northern Tasman Sea will remain unsettled, with lower pressures than normal, bringing the likelihood of significant rainfall events to the North Island and the upper South Island.

MARCH BY THE NUMBERS:

- The highest temperature was 31.8C, observed at Kawerau on March 5.

- The lowest temperature was -1.8C, observed at Middlemarch on March 17.

- The highest 1-day rainfall was 205 mm, recorded at Secretary Island on March 19.

- The highest wind gust was 176 kmh, observed at Cape Foulwind on March 13.