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Why does wind swirl round a storm instead of blowing straight in?
Weather Patterns lab · Last updated: 16 October 2026
You watch wind rush towards the low pressure at the heart of a storm and find that it does not blow straight in. Instead it curves and swirls round the centre. They find out how Earth's spin bends the wind, which is why cyclones over the Bay of Bengal always turn the same way.
What you'll discover
- Wind blows from areas of high pressure towards areas of low pressure.
- Earth's rotation bends moving air to the right in the northern hemisphere and to the left in the southern.
- This bending makes storms in the north spin anticlockwise and storms in the south spin clockwise.
The science in plain words
Air moves from where the pressure is high to where it is low, and that moving air is wind. A storm forms around a centre of low pressure, often where warm, moist air is rising. You might expect air to rush straight into the centre and fill it up, but on a spinning planet it cannot.
Earth rotates, and the ground near the equator moves eastwards faster than the ground near the poles. Air travelling over long distances keeps its own motion while the Earth turns beneath it, so from the ground its path seems to curve. This apparent push is called the Coriolis effect. In the northern hemisphere it turns moving air to the right; in the southern hemisphere, to the left.
As air flows towards a low, it keeps being turned aside, so instead of reaching the centre it starts to circle around it. In the northern hemisphere, storms such as the cyclones over the Bay of Bengal spin anticlockwise when seen from above. In the southern hemisphere they spin clockwise. Air near the ground still spirals slowly inwards because friction slows it, and it rises in the centre, forming clouds and rain. The Coriolis effect is almost zero at the equator, which is why tropical cyclones rarely form very close to it. It is far too weak to decide which way water drains from a sink.
Where it fits
- India, NCERT: Class 8 science, Chapter 6: Pressure, Winds, Storms, and Cyclones
- United States: Grades 6 to 8
- Next Generation Science Standards: MS-ESS2-5, MS-ESS2-6
Common questions
Why do cyclones spin?
Air rushes towards the low pressure at a cyclone's centre, but Earth's rotation turns moving air aside, an effect called the Coriolis effect. Instead of flowing straight in, the air circles the centre. In the northern hemisphere cyclones spin anticlockwise, and in the southern hemisphere clockwise.
What is the Coriolis effect?
The Coriolis effect is the way moving air and water appear to curve because Earth is spinning underneath them. It turns winds to the right in the northern hemisphere and to the left in the southern hemisphere. It is strongest near the poles and absent at the equator.
Does water go down the drain the other way in Australia?
Not because of Earth's spin. The Coriolis effect matters for huge, slow systems like storms, but in a sink or toilet it is far too weak. The direction water swirls depends on the shape of the basin and how the water was moving.
Related labs
- Tornado Formation: Why does air spin faster and faster as it rushes into a tornado?
- Ocean Currents: Ice at one end, warmth at the other: how does a whole ocean start to move?
- Water Cycle: The Sun lifts water out of the sea. Where does it go, and how does it get back?
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Try it yourself
The Weather Patterns lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.