NZ's 'unprecedented marine heatwave' from 2017 set to repeat this summer

The National Institute of Water and Atmospheric Research (NIWA) says warmer sea temperatures in the Tasman could put New Zealand at risk of more tropical cyclone activity this year.

A comparison of sea surface temperatures on October 27 in 2017, and in 2020. Source: NIWA

NIWA's weather forecasting department said last night that sea surface temperatures this year are warmer in 2020 than they were three years ago in 2017, when New Zealand's coastal water "experienced an unprecedented marine heatwave".

According to NIWA, the higher temperatures could mean more energy to power cyclones, and that New Zealand now has an "elevated" risk of ex-tropical cyclone activity during this cyclone season, which runs from November to April.

The forecaster has produced its latest tropical cyclone outlook, concluding that New Zealand, along with New Caledonia, will face an "elevated" risk of tropical cyclones, with 1-2 ex-tropical cyclones expected to affect Aotearoa this season, and 3-4 in New Caledonia.

NIWA principal scientist for forecasting and media Chris Brandolino said "this is an important reminder that all communities should remain vigilant and follow forecast information provided by their national meteorological service".

Meteorologist Ben Noll said the modeling was based on finding "analogue" seasons in South Pacific weather history - seasons which are very similar to the current one within the past 50 years.

They identified five seasons which had very similar La Niña or oceanic conditions, and based this year's forecast off those.

Among those analogue seasons was 2017-18, which produced Cyclones Gita and Fehi.

Those two ex-tropical cyclones impacted New Zealand in the late season, bringing strong winds and flooding, leading to insurance claims totalling about $65 million, according to the Insurance Council.

For a full forecast for your area, see our weather page here.