Widespread Flash Flooding Hits Wellington

Emergency services responded to over 150 weather-related calls after more than 70mm of rain fell in one hour in parts of southern Wellington.

On Monday morning, Wellington experienced widespread flash flooding. MetService reported the intense rainfall, which led to multiple sections of local state highways being closed due to flooding and slips, severely disrupting transport services. In response, hubs were set up in Lower Hutt to support displaced residents.

Event Description

Rainfall totals over a 48-hour period nearly tripled monthly averages for the area. Some residents described it as the worst flooding event since a storm in 1976. In some suburbs, streets were flooded and vehicles were affected by floodwaters.

Meteorological Context

The flooding was caused by a large, slow-moving low-pressure system that developed over the Southern Ocean. The system drew cold air north over unusually warm seas in the Tasman Sea, generating widespread convection and thunderstorms that produced heavy, localized downpours.

Forecasters identified the risk of severe weather in advance, but pinpointing the exact locations of the heaviest rain was difficult due to fine-scale atmospheric dynamics. Converging winds along the south coast helped hold intense rainfall over specific areas for extended periods.

This event followed Cyclone Vaianu, which had saturated the ground in many parts of the North Island, increasing runoff and contributing to the severity of the flooding.

Broader Context

A University of Waikato modeling study projects that under a mid-range emissions scenario, the most intense rainfall events across much of New Zealand could increase by 10–20% by the second half of the century.

As sea and air temperatures rise, more moisture is held in the atmosphere, which can provide additional fuel for storms to produce heavier rainfall.