Tropical cyclones form from clusters of persistent thunderstorms. These thunderstorms draw a great amount of air from the lower levels and vent it high into the atmosphere, leaving less air and lower air pressure at the surface.
A tropical cyclone grows from a depression into a storm, then into a full-blown hurricane, as the long-lived thunderstorms gather strength around the center of low pressure.
The thunderstorms at the center of the storm strengthen when they pass over warmer waters and weaken when they pass over cooler waters. However, tropical cyclone intensity is not as simple as a temperature difference between the air and the water. Latent heat release is the key to the intensity of a hurricane.
Strong winds in a developing storm scrape across the surface of the sea and evaporate some of that warm ocean water, transferring that warmth into water vapour in the air. This vapour travels up into the thunderstorms and condenses into clouds, releasing its heat and giving the storm instability.
Warmer waters release more heat through evaporation, which results in stronger thunderstorms, which then intensifies the tropical cyclone and its winds. Stronger winds lead to more evaporation, triggering more heat release into the storm, continuing the feedback cycle.
This process only stops when the storm’s structure is disrupted – by dry air, wind shear, or interaction with land – or when it encounters cooler waters. Lower sea surface temperatures don’t release enough heat to fuel the thunderstorms around the center of the tropical cyclone, causing it to lose strength.