As long as there’s a supply of warm water, the thunderstorm sustains itself, converting moisture into sheeting rain and downdraft winds. Other thunderclouds might line up along the leading edge of a cold front into a “squall line,” a towering convective engine that stretches from horizon to horizon. Hurricanes start when a slight kink—a disturbance in the trade winds, a dust storm blowing out to sea off the Sahara—develops in the upper-level air. The squall line starts to rotate around the kink, drawing in warm, volatile air and sending it up the gathering vortex at its center. The more air
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