"What Is the Fujiwhara Effect? Explain Its Impact on the Movement and Intensity of Tropical Cyclones" — UPSC Mains 2026 GS1
A complete, examiner-standard 150-word model answer for the UPSC Mains 2026 GS Paper 1 question on the Fujiwhara effect — with pointer-based structure, an orbit diagram, static core content, and the November 2025 Bay of Bengal current affairs linkage.
UPSC Mains 2026 GS Paper 1 asked candidates to explain the Fujiwhara effect and its impact on the movement and intensity of tropical cyclones, within a strict 150-word limit. Below is a full model answer in pointer-and-diagram format, along with a static-portion refresher and the relevant late-2025 current affairs hook.
"What is the Fujiwhara effect? Explain its impact on the movement and intensity of tropical cyclones." (150 words)
Model Answer
Introduction
The Fujiwhara effect, first described by Japanese meteorologist Sakuhei Fujiwhara in 1921, occurs when two nearby tropical cyclones — typically within about 1,400 km of each other — begin orbiting a common centre due to the mutual interaction of their wind circulations.
Body
(Stronger)
(Weaker)
Orbit
Both rotate around shared centre, then drift apart
Merger
Weaker cyclone absorbed; single, often stronger system forms
Ejection / Dissipation
One storm flung away, or weakens from moisture starvation
- Proximity threshold — interaction becomes significant when tropical cyclones close to within ~1,400 km; extratropical systems interact at larger distances (~2,000 km).
- Mutual wind circulation — each cyclone's rotating wind field advects the other, causing both centres to circle a shared point — counter-clockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.
- Erratic, hard-to-predict paths — cyclones may loop, stall, or deviate sharply from their model-forecast track, unlike the smooth curves of a lone system.
- Prolonged landfall impact — stalling during interaction can extend the duration of rainfall over one region, raising flood risk.
- Merger scenario — when centres close in fully, vortices can fuse into a single larger cyclone with enhanced convection, stronger winds and higher storm-surge risk.
- Weakening scenario — competition for warm, moist inflow can starve the smaller cyclone of energy, causing rapid weakening or dissipation even as the dominant one intensifies.
- November 2025 Bay of Bengal case — forecast models flagged a possible Fujiwhara interaction between two developing systems, raising flood risk across Tamil Nadu, Andhra Pradesh, Odisha, West Bengal, Sri Lanka and Myanmar.
- Forecast uncertainty — such interactions delay confident landfall predictions, complicating IMD/NDMA evacuation and relief planning.
Conclusion
Though rare, the Fujiwhara effect significantly increases uncertainty in cyclone track and intensity forecasting, making it an increasingly important consideration for disaster preparedness as warming seas raise the odds of closely clustered tropical systems.
Named after Sakuhei Fujiwhara (1921 paper, building on an 1889 Japanese study); also called "binary interaction." Interaction thresholds: tropical cyclones ~1,400 km, extratropical cyclones ~2,000 km; rotation rate accelerates within ~650 km; merger/shearing typical within ~300 km.
Four possible outcomes: orbit-and-separate, merger, ejection, dissipation. Historical examples: Hurricanes Iris–Humberto (1997 Atlantic season); Cyclones Odette–Seroja (Southern Hemisphere, April 2021); Hurricanes Humberto–Imelda (Atlantic, September 2025).
Answer Writing Tips for This Question
- Draw a simple two-circle orbit diagram on the answer sheet — this question is a textbook case where a quick sketch communicates the mechanism faster than a sentence.
- The question has two explicit asks — movement AND intensity — so split the body into two clearly separate pointer-groups; don't blend them into one list.
- Give both possible outcomes for intensity (merger → strengthening; competition → weakening) — a one-sided answer misses half the marks available.
- Add the proximity threshold figure (~1,400 km) — a precise number signals stronger command of the concept than a vague "when two cyclones come close."
- Anchor with a current or recent example (here, the November 2025 Bay of Bengal case) to show the concept isn't just textbook trivia but active forecasting reality.
- Close by linking to disaster management — UPSC GS1 physical geography answers score higher when tied to real-world administrative relevance.
