Word count (not including references or opening paragraph): 2,000 Climate change may bring new hazards through novel combinations of extreme weather (compound events) 1. Here we evaluate the possibility of dangerous heat following major tropical cyclones (TCs)-a combination with serious potential consequences given that mega-blackouts may follow powerful TCs 2 , and the heavy reliance on air conditioning 3. We show that "TC-heat" events are already possible along densely populated coastlines globally but, so far, only an estimated 1,000 people have been impacted. However, this number could rise markedly, with over two million at risk under a storyline of the observed TCs recurring in a 2°C warmer world than preindustrial. Using analogues as focussing events we show, for example, that if the catastrophic 1991 Bangladesh Cyclone occurred with 2°C global warming, there would be >70% chance of subsequent dangerous heat. This research highlights a gap in adaptation planning and a need to prepare for an emerging TC-heat compound hazard. Extreme heat is a major threat to public health and a risk that is projected to rise with global warming 4 , even if temperatures are held below the Paris targets of 1.5 or 2°C 5. With around 1.6 billion units in operation, air conditioning (AC) reduces vulnerability to extreme heat 3,6. However, populations dependent on AC may become highly exposed in the event of power failure 7. Significant electricity outages have already been caused by Tropical Cyclones (TCs), with the top three events (2013 Typhoon Haiyan, 2017 Hurricane Maria, and 2012 Typhoon Bopha) incurring between 3.2 to 6.1 billion customer-hours of lost supply over one or two months 8-11. Significant heat-related mortality was not reported during these mega-blackouts, but given the rapid rise in dangerous humid heat projected at low-latitudes 4 , we identify the growing threat of a catastrophic "TC-heat" compound hazard. In this storyline, a TC first cripples electrical infrastructure, then is followed by deadly heat as the population tries to recover. Here, we provide the first assessment of the present and evolving risk of the TC-heat