The factors that influence the size of tropical cyclones (TCs) are not completely understood. High-resolution numerical simulations of hurricane Catarina in the South Atlantic indicate that the TC size increases proportionally to the surface latent heat flux, when atmospheric and sea surface temperature (SST) are increased. The TC size is defined as the area enclosed by three wind thresholds: gale-force winds, damaging-force winds and hurricane-force winds. The enlargement increases sharply with the wind threshold. Depending on the wind threshold, the area can increase by more than an order of magnitude when air and sea temperature are both increased by 2 °C. There is a clear linear relationship between the size increase and the latent heat flux during the TC lifetime. The size effect is driven initially by the enhanced air–sea moisture contrast and the surface winds become predominant only in the later stages. Temperature changes may therefore have a profound impact on cyclone size.