The March of the Monsoon

On the morning of May 13, 2025, the India Meteorological Department announced that the southwest monsoon had reached the south Bay of Bengal and the Andaman Sea. Hours later, showers swept across Tamil Nadu and Karna­taka—early arrivals from a season that, if it holds course, will touch down in Kerala by May 27, making it the earliest onset in 16 years. The last time it came this soon was in 2009, a year that opened with promise and closed in drought.

Each year, this seasonal arrival is more than meteorological housekeeping—it is India’s true new year, a clock set not by the calendar but by pressure gradients, ocean temperatures, and hope. The southwest monsoon, which spans June through September, brings over three-quarters of the country’s annual rainfall. It waters fields, recharges aquifers, fills hydroelec­tric dams, and sets the tempo of rural life. A generous season can lift agricultural incomes, ease inflation, and nudge up GDP. A stingy one can empty reservoirs and roil politics.

Yet, the monsoon has never been punctual, or predictable. It arrived 10 days late in 2016; it arrived early in 2013 and flooded Uttarakhand. In 1918, it burst in mid-May and brought deluge; in 2002, it all but failed. Its course is mapped through what meteorologists call the “march of the isochrones”— the line that traces its staggered northward advance from Kerala to Kashmir, pausing, surging, sometimes circling back.

Recent decades have seen a quiet revolution in monsoon science. Where forecasters once relied on Himalayan snow and surface pressure, they now parse sea surface temperatures, Pacific typhoons, jet streams, and remote atmospheric waves. The monsoon, it turns out, responds to distant whispers: a cyclone near the Philippines can stall it; a warmer Arabian Sea can strengthen it.

And yet, for all the models and satellites, it remains a force only partly understood. Its rains have become more intense, more erratic, more localised. Its behav­iour shifts with climate change. But its meaning endures.

Andaman and NicobarBay of BengalKarnatakamonsoonTamil Nadu