Observed Linkages Between Marine Heatwaves and Extreme Weather Over Land: A New Zealand Case Study

ABSTRACT Marine heatwaves (MHWs) are increasingly prevalent oceanic extremes with the potential to influence adjacent weather and climate over land. This study characterizes the spatio‐temporal variability of MHWs surrounding New Zealand from 1982 to 2020 and examines their relationship with concurrent terrestrial temperature and rainfall anomalies, alongside the broader synoptic‐scale circulation. This observational analysis reveals a marked spatial contrast: short‐lived, high‐intensity MHWs dominate the Tasman Sea, whereas longer‐duration events occur in the southeastern offshore region under conditions of persistent high‐pressure systems and reduced wind. Composite and case study analyses of the five most significant events demonstrate that MHW impacts over land are strongly conditioned by atmospheric circulation. All events produced substantial national warming over land (+2°C), confirming a robust thermodynamic coupling between the ocean and land surface. In contrast, rainfall responses are highly variable and depend strongly on synoptic‐scale circulation. Extreme precipitation occurs when atmospheric rivers (AR) or ex‐tropical cyclones interact with anomalously warm ocean conditions, whereas persistent anticyclonic regimes favour widespread dryness despite the presence of a MHW. These results indicate that MHWs primarily act as thermodynamic modifiers of the lower atmosphere, increasing heat and moisture availability, while atmospheric circulation governs the timing, location, and magnitude of rainfall extremes. The findings highlight the importance of considering both oceanic and atmospheric drivers when assessing compound climate extremes in New Zealand.