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How IMD Declares the Monsoon Onset over Kerala and Monitors Its Advance Across India

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Cover image: Monsoon clouds enveloping the Western Ghats near Lavasa, Maharashtra, during the southwest monsoon season. [Photo: Satyaban B Ratna] Introduction Every year, the arrival of the southwest monsoon is one of the most eagerly awaited weather events in India. Farmers prepare for sowing, reservoirs await replenishment, and millions of people look forward to relief from the intense summer heat. Consequently, considerable attention is paid to the announcement of the monsoon onset over Kerala, which marks the official beginning of the rainy season over the Indian mainland. The onset of the southwest monsoon over Kerala (MOK) is considered the official commencement of the monsoon season over the Indian mainland. It serves as an important meteorological milestone and provides the starting point for monitoring the advance of the monsoon across different regions of the country. The normal date of monsoon onset over Kerala is 1 June , although the actual onset date may vary from year to...
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What Does IMD's Probabilistic Monsoon Forecast Really Mean?

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Introduction Every year, when the India Meteorological Department (IMD) releases its seasonal monsoon forecast, one common question immediately follows: “So, will the monsoon definitely be good or bad this year?” This year, many students, friends, weather enthusiasts, and members of the public asked similar questions after seeing IMD’s probabilistic monsoon forecast map. At first glance, the map may look confusing because it uses probabilities instead of giving a simple “yes” or “no” answer. However, this probabilistic approach is one of the most scientifically meaningful ways to describe seasonal monsoon forecasts. Unlike a daily weather forecast, which predicts conditions over the next few days, a seasonal monsoon forecast describes the likelihood of different rainfall outcomes several months in advance. Understanding this distinction is the key to interpreting the forecast correctly. Figure 1. Probabilistic forecast of rainfall categories (Below Normal, Normal, and Above Normal) o...
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El Niño Does Not Always Mean “No Rain” During the Monsoon: Can Better Water Management Reduce Its Impacts?

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When people hear about an El Niño year, the common perception is often straightforward: weak monsoon, drought, and severe rainfall deficiency across India. While El Niño can indeed suppress the Indian summer monsoon, the reality is often more nuanced. The figure below shows the distribution of rainy days across India during nine major El Niño years between 1982 and 2023. An interesting feature clearly emerges: many parts of India continue to experience a considerable number of rainy days even during El Niño years. Figure:  Rainy-day distribution during major El Niño years over India. Even during deficient monsoon years, many regions continue to receive considerable rainy-day activity. This observation carries an important message. A deficient monsoon season does not necessarily mean that it never rains. In many cases, rainfall may still occur on several days, but the total seasonal rainfall becomes lower because: rainfall intensity is weaker, rain events are unevenly distribut...
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A Possible El Niño in 2026: What It Could Mean for the Indian Monsoon

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Every year, the Indian monsoon is watched closely—not only by meteorologists, but by farmers, water managers, disaster agencies, businesses, and millions of ordinary citizens. The southwest monsoon provides nearly 70–80% of India’s annual rainfall (Figure 1) and supports agriculture, water resources, energy production, and livelihoods. This year, growing discussions around the possible development of an El Niño in the Pacific Ocean have raised an important question: Will El Niño affect India’s monsoon in 2026? Figure 1: Average monsoon season (June-September) rainfall (left panel) and Percentage of annual rainfall during monsoon season (right panel) The short answer is: possibly, but not always in a straightforward way. To understand what may happen, it is useful to look at the science behind El Niño, its historical relationship with the Indian monsoon, and why modern forecasting is more nuanced than simple cause-and-effect. What is El Niño? The El Niño–Southern Oscillation (ENSO) is...
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El Niño, La Niña and the Indian Monsoon: A Climate Story from the Pacific Ocean to India

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Introduction Every few years, changes in ocean temperatures thousands of kilometers away in the tropical Pacific Ocean capture global attention. Terms such as El Niño , La Niña , and even Super El Niño begin appearing in weather and climate forecasts and news headlines. These phenomena are part of the El Niño–Southern Oscillation (ENSO), one of the most important drivers of year-to-year climate variability on Earth. But what do these terms mean, and how can changes in the distant Pacific Ocean influence the Indian monsoon? The answers lie in a fascinating scientific story that connects the Pacific Ocean, the Indian monsoon, and the pioneering work of Sir Gilbert Walker, who sought to unlock the secrets of monsoon prediction while serving in India more than a century ago. What are El Niño and La Niña? El Niño and La Niña are opposite phases of the El Niño–Southern Oscillation (ENSO), a naturally occurring ocean-atmosphere phenomenon in the tropical Pacific Ocean. El Niño El Niño occurs...
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