Northland Regional Council has supported a new report, developed in collaboration with the University of Auckland, examining two major extreme weather events that affected the region in February 2023—Cyclone Gabrielle and the Mangawhai flash flood.
This study examines the atmospheric drivers of extreme storms in Northland, including atmospheric rivers, tropical cyclones, ENSO conditions, and local summer heating. It analyses historical rainfall patterns to establish how these 2023 events compare to Northland's typical storm characteristics and compares how these events fit within regional storm patterns. Using ground-based rainfall gauges, weather radar, and satellite observations, the report provides a detailed spatial and temporal analysis of rainfall distribution during both events.
Key findings show that Cyclone Gabrielle delivered widespread rainfall exceeding historical February maxima at many stations, causing significant river flooding particularly in southern areas. By contrast, the Mangawhai event was highly localised, with intense rainfall concentrated over a short duration, triggering rapid flash flooding.
Analysis of historical storms shows that extreme rainfall in Northland often occurs during the middle stages of storm events. Both the 2023 events followed this pattern, with peak rainfall occurring during the main period of each storm.
The analysis highlights that atmospheric rivers are an important contributor to extreme rainfall in Northland, helping to explain the widespread rainfall observed during major storm events.
The report also quantifies impacts across housing, roads, power systems, water infrastructure, and communications networks.
Overall, the report provides a stronger evidence base to support improved flood management and infrastructure planning across Northland.
Published: 25 Jun 2026