How Tropical Cyclones Form

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Warm Ocean Water

Tropical cyclones require sea surface temperatures above 26.5°C (80°F) to form. Warm ocean water provides the heat energy that drives these storms through evaporation and condensation. The deeper the warm water layer, the more fuel available for intensification.

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Coriolis Effect

The Coriolis effect, caused by Earth's rotation, is essential for tropical cyclone formation. It causes cyclones to spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. This force is weakest near the equator, which is why tropical cyclones rarely form within 5 degrees latitude of the equator.

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Saffir-Simpson Scale

The Saffir-Simpson scale rates tropical cyclones from Category 1 to 5 based on wind speed. Category 1: 119-153 km/h. Category 5: over 252 km/h. Category 3 and higher are major hurricanes. The scale primarily measures wind hazard; storm surge and flooding often cause more fatalities.

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Storm Naming

Tropical cyclones are named from lists maintained by the World Meteorological Organization. Atlantic names repeat every six years unless retired. Northwest Pacific names are contributed by 14 member nations. Names of deadly storms are retired out of respect for victims.

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Life Cycle

A tropical cyclone passes through stages: begins as a tropical disturbance, becomes a tropical storm at 63 km/h, intensifies to hurricane/typhoon at 119 km/h, peaks, then weakens due to landfall, cooler waters, or wind shear. Some become extratropical.