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Independent guide

How hurricanes work

How hurricanes form, what the eye and eyewall do, and why wind category does not describe every hazard.

The short version

A hurricane is a large rotating storm powered by heat and moisture from warm ocean water. Wind is only one hazard: rain, flooding and dangerous seas can affect places far from its centre.

How a storm gets its energy

Warm ocean, rising air, clouds and heatWarm ocean water supplies moisture. Moist air rises and condenses into clouds, releasing heat. Air flows inward near the surface. Simplified side view, not a forecast. Clouds release heatAir flows inAir flows in Warm ocean supplies moisture
How energy enters a storm. Simplified side view; favourable atmospheric conditions are also needed.

  1. A disturbance starts it

    A cluster of thunderstorms or a tropical wave provides a starting point. Most disturbances never become hurricanes.

  2. Warm water supplies moisture

    Warm, moist air rises. Air flows inward beneath it toward an area of lower pressure.

  3. Clouds release heat

    As water vapour turns into cloud droplets, it releases heat. This helps keep air rising and thunderstorms growing.

  4. The storm becomes organised

    The storm can strengthen when conditions allow. Large changes in wind speed or direction at different heights—called wind shear—can disrupt it.

Source: NOAA · How hurricanes form ↗

Hurricane, typhoon or cyclone?

These are regional names for the same broad kind of storm. In the Atlantic and eastern/central North Pacific, a tropical cyclone becomes a hurricane at sustained winds of 74 mph (119 km/h, 64 knots). Other regions use different naming and intensity systems; do not compare their categories as though they were identical.

The eye is not the whole storm

The eye can be relatively calm. The surrounding eyewall contains intense thunderstorms and strong winds; rainbands extend much farther out. A lull does not mean it is safe to go outside. Wait for local authorities to say it is safe.

Source: HI-EMA · Hurricanes and their hazards ↗

What the category tells you—and what it doesn’t

The Saffir–Simpson scale rates hurricanes from 1 to 5 by maximum sustained wind speed. It does not measure rainfall flooding, storm surge or tornado risk. A lower-category or weakening storm can still be extremely dangerous.

Source: NHC · Hurricane Wind Scale (PDF) ↗

Why “offshore” does not mean “no impact”

Large waves, strong currents and rain can extend far from a storm’s centre. Distance to land is useful context, not a safety boundary or a countdown to impact.

Understand what each map can—and cannot—tell you →

Sources checked September 4, 2026. General guidance; follow local emergency instructions.