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A deep area of low pressure to the south-east of New Zealand’s North Island swept into the region on Sunday, bringing heavy rain, gale-force winds and dangerous coastal swells that lashed exposed shorelines. The storm triggered power outages, forced evacuations, and damaged infrastructure, with further impacts likely on Monday as the system lingers for a time, before tracking southwards later.
Its arrival came after days of widespread flooding in the Ōtorohanga district, where a man was found dead after his vehicle became submerged in flood waters. Some areas recorded more than 100mm of rain in 24 hours on Thursday, with Gisborne, Hawke’s Bay and the Bay of Plenty bearing the brunt of the deluge. The Tararua district and Wairarapa have also been experiencing heavy rain and strong winds from the storm, with 24-hour rainfall totals reaching more than 100mm locally, and wind speeds of about 80mph (130km/h) along coastal parts.
The unusually persistent system developed when a cold front tracking east across the country late last week merged with a strengthening low-pressure system offshore, causing it to deepen. It then became trapped between two blocking high-pressure systems, stalling in place and subjecting the same communities to prolonged heavy rain.
A humid air mass of tropical origin has fed additional moisture into the storm, further intensifying downpours. The low is now looping back on itself, a movement that continues to funnel rain bands over the already saturated area, compounding the risk of further flooding.
Meanwhile, Storm Nils battered western Europe last week with what Météo-France described as “uncommon strength”, leaving two people dead in France and cutting power to about 900,000 homes. Flood alerts remained in place across south-west France, while red alerts were issued in northern Spain, including Galicia, Cantabria, and the Basque Country. Winds of up to 100mph lashed France’s Atlantic coast and the Alps, increasing avalanche danger in Alpine ski resorts. In the Italian Alps, unstable snowpack has been blamed for a number of deaths, including incidents in areas close to the Winter Olympics, though venues remained opened under close monitoring.
In Portugal, a motorway bridge collapsed after the Mondego River burst its banks following weeks of relentless rain that left soils saturated and rivers swollen. Transport networks across Spain, France, and Portugal were heavily disrupted, with flight cancellations and rail delays amid flooding and high winds.
The storm was intensified by a pronounced southward dip in the jet stream, steering a powerful Atlantic low into western Europe. As mild moisture-laden ocean air collided with colder continental air, the sharp temperature contrast fuelled the system. Rapid uplift generated intense rainfall at lower elevations and heavy snowfall over the Alps, where fresh snow and strong winds significantly increased avalanche risk.
