In the summer of 2013-14, an unprecedented marine heatwave occurred in the south-eastern Atlantic. This co-occurred with drought in eastern South America and outbreaks of dengue fever. The combined terrestrial-marine extreme event was driven by a blocking high pressure system which prevented the passage of synoptic systems and the normal development of the South Atlantic Convergence Zone that brings rain to the region during summer. Over the ocean, the high-pressure system was associated with reduced cloud cover - thereby increasing solar radiation - and weaker winds - that reduced the turbulent heat loses from the ocean.

Based on observational data from the last few decades, we show that these atmospheric conidiations typically prevail during MHW events in this region and that the blocking high is part of a planetary wave train triggered by convection associate with the passage of the MJO in the tropical Info Pacific. We also find a consistent reduction in marine primary productivity associated with these regional MHWs