How does a cluster of thunderstorms turn into a hurricane?

A hurricane starts as a cluster of ordinary thunderstorms over very warm ocean that learns to feed itself. Over the warm tropical sea, air is heated and rises in parcels, which makes towering thunderstorms. These showers dissipate quite quickly, but they can group together into large clusters. That creates a flow of warm, moist, rapidly rising air, which starts to rotate as it interacts with the rotation of the Earth.

Not every cluster makes it. The thunderstorms need sea surface temperatures of around 27 °C, low vertical wind shear, atmospheric instability, high humidity in the lower to middle troposphere, enough Coriolis force to develop a low-pressure center, and a pre-existing low-level disturbance. Because the Coriolis force is needed, cyclones rarely form within 5 degrees of the equator.

The fuel is the ocean itself. A tropical cyclone derives its energy from the evaporation of water from the ocean surface, which condenses into clouds and rain when moist air rises and cools. This differs from mid-latitude storms such as nor'easters and European windstorms, which are powered primarily by horizontal temperature contrasts. Heat energy from the ocean acts as the accelerator, which is why inland regions suffer far less damage than coastal ones, although flooding is felt across the board.

Once mean surface winds pass 35 knots, a tropical cyclone is deemed to have formed, and it is assumed to be self-sustaining. The name depends on where it happens: a hurricane in the Atlantic or northeastern Pacific, a typhoon in the northwestern Pacific.

At the center of a mature storm, the weather in the eye is normally calm, although the sea may be extremely violent.