Tropical cyclones are carried by the large-scale wind patterns that govern the atmosphere. These storms form over warm ocean waters, where the sea surface temperature is about 26º C or more, providing the heat and moisture they need to grow. But once they have formed, the way they move depends entirely on the winds that surround them, much like a leaf swept along by a river.

The tropical areas where cyclones develop are roughly between 5º and 20º north and south (of the equator). Here the dominant winds are the trade winds, which blow from east to west throughout the year as part of the global Hadley circulation. This is a global convection pattern driven by the uneven heating of the earth: warm air rises near the equator, moves towards the poles, cools and sinks around the 30º latitude,

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