Why in the News?

The Fujiwhara Effect was asked in the UPSC Civil Services Mains 2026, GS Paper 1, where candidates were asked to explain the phenomenon and its impact on the movement and intensity of tropical cyclones.

The concept is important because tropical cyclones do not always behave as isolated systems. When two cyclonic systems come sufficiently close, their circulation can begin to influence each other, producing an unusual interaction known as the Fujiwhara Effect.

What is the Fujiwhara Effect?

The Fujiwhara Effect refers to the mutual interaction of two nearby tropical cyclones, in which the cyclones begin to rotate around a common centre.

The phenomenon was described by Japanese meteorologist Sakuhei Fujiwhara in 1921, who studied the interaction between two vortices in a fluid.

In simple terms, when two tropical cyclones come close enough, their wind fields start interacting. Instead of continuing independently, the systems can begin a kind of “cyclonic dance” around a common centre. The interaction may eventually lead to deflection, separation or even the absorption of one cyclone by the other.

How does the Fujiwhara Effect occur?

The interaction generally develops when two tropical cyclones are sufficiently close for their circulation systems to influence one another.

The major stages can be understood as:

1. Approach: Two tropical cyclones move towards each other.

2. Mutual interaction: Their circulation and steering fields begin to interact.

3. Rotation: The systems may orbit around a common centre, with the centre influenced by their relative size and strength.

4. Possible outcomes: Depending on their intensity and distance, the cyclones may separate, change direction, or one may eventually absorb the other.

Impact on the Movement of Tropical Cyclones

The Fujiwhara Effect can significantly disturb the normal track of tropical cyclones.

– Change in direction: A cyclone may deviate from its expected path.

– Curved or looping tracks: Mutual rotation can produce unusual trajectories.

– Change in speed: Interaction may alter the translational speed of one or both systems.

– Absorption: If one cyclone is considerably stronger, the weaker system may be drawn into the stronger circulation.

– Forecasting uncertainty: Such changes make the prediction of cyclone landfall more challenging.

Thus, a cyclone that appears to be following a predictable path can behave differently once another nearby system becomes influential.

Impact on Cyclone Intensity

The Fujiwhara Effect does not always produce the same intensity outcome.

In some cases, interaction can weaken a cyclone by disrupting its circulation or affecting its access to favourable atmospheric and oceanic conditions. In other situations, interaction or eventual merger can lead to a more consolidated circulation.

Therefore, the effect can result in:

Weakening → disruption of circulation → absorption → or possible intensification after interaction.

The final outcome depends on factors such as the relative strength and size of the cyclones, their distance, environmental wind shear and surrounding atmospheric conditions.

Examples

The phenomenon has been observed in different ocean basins. For instance, Cyclone Saroja and Cyclone Odette interacted near Western Australia in 2021, while tropical systems such as Hilary and Irwin have also been cited in discussions of Fujiwhara interaction.

Such cases demonstrate why interactions between multiple cyclones are important for modern weather forecasting.

Why is it Important for India?

For India, understanding cyclone interaction is particularly relevant because the Bay of Bengal and Arabian Sea regularly witness tropical cyclone activity.

A Fujiwhara-type interaction can complicate:

– cyclone-track prediction,

– landfall forecasting,

– intensity estimation,

– early-warning systems, and

– disaster-management planning.

For coastal states, even a relatively small change in a cyclone’s track can significantly alter the area exposed to strong winds, storm surge and heavy rainfall.

UPSC Perspective

The Fujiwhara Effect is a good example of how UPSC can transform a seemingly technical geographical concept into an analytical question.

For Mains, remember the concept through a simple framework:

Definition → Mechanism → Impact on Movement → Impact on Intensity → Example → Disaster-management relevance

The key is not merely to define the term. A good answer should explain why two cyclones interact, how their tracks change and what happens to their intensity.

Conclusion

The Fujiwhara Effect highlights the complex and dynamic nature of tropical cyclones. When two powerful atmospheric systems interact, their behaviour can become considerably less predictable. For meteorologists and disaster-management agencies, understanding such interactions is therefore crucial for improving cyclone forecasting, early warning and coastal disaster preparedness.

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