Southwest monsoon to be 8% below Long Period Average: IMD

IMD's April 2026 long-range forecast places the southwest monsoon at 92% of the Long Period Average — 8 percentage points below the normal threshold. The for...

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What Happened

IMD's April 2026 long-range forecast places the southwest monsoon at 92% of the Long Period Average — 8 percentage points below the normal threshold.
The forecast puts the season in the "below normal" band; the probability of deficient rainfall (below 90% LPA) is estimated at 35%, against a historical average of 16%.
IMD is scheduled to issue an updated, more granular forecast in May 2026, which will include spatial distribution and monthly breakdowns.
Private forecaster Skymet has issued a corroborating estimate of 94% LPA, also classifying 2026 as a below-normal season.
Both agencies flag developing El Niño conditions in the equatorial Pacific as the primary risk factor, with weakness concentrated in the August–September window.

Static Topic Bridges

IMD's Long-Range Forecasting Methodology

The India Meteorological Department uses a two-stage statistical–dynamical ensemble modelling system for seasonal monsoon forecasts. The April forecast uses a limited set of global climate predictors; the May update incorporates additional predictors for more regional precision. IMD transitioned from purely statistical models to a coupled ocean–atmosphere general circulation model (CFS v2) as its primary tool in recent years.

Forecast issued in two phases: Phase 1 (April) — seasonal outlook with national-scale probabilistic estimate; Phase 2 (late May) — regional forecasts for four broad monsoon zones.
Key predictors include: ENSO/SST anomalies in the Pacific, Indian Ocean Dipole (IOD), Eurasian snow cover extent (January–March), and North Atlantic SST anomalies.
The ±5% error margin means the 92% forecast could range from 87% to 97% of LPA.
Below-normal snow cover over Eurasia in January–March 2026 (a historically positive signal for monsoon performance) partially offsets the El Niño signal.

Connection to this news: Understanding how IMD constructs its forecasts helps contextualise the 92% estimate — the model reconciles competing signals (negative El Niño, partially positive snow cover, neutral IOD transitioning to positive) to arrive at a probabilistic outcome.

Indian Ocean Dipole (IOD) as a Monsoon Modulator

The Indian Ocean Dipole is a coupled ocean-atmosphere phenomenon characterised by a gradient in sea surface temperatures (SST) between the western and eastern Indian Ocean. A positive IOD (warmer western, cooler eastern Indian Ocean) generates enhanced convection over the western Indian Ocean and Arabian Sea, boosting moisture supply to the Indian monsoon — partially counteracting El Niño.

IOD phases are measured by the Dipole Mode Index (DMI), the difference in SST anomaly between the western (50°E–70°E, 10°S–10°N) and eastern (90°E–110°E, 10°S–0°) Indian Ocean boxes.
Positive IOD years (e.g., 2019) have produced above-normal monsoon rainfall even during mild El Niño episodes.
IMD forecasts a transition to positive IOD by the end of the 2026 monsoon season — a potentially mitigating factor, though too late to rescue August–September totals.
Negative IOD (cooler west, warmer east) amplifies El Niño's suppressive effect on the monsoon.

Connection to this news: The forecast of positive IOD development toward the season's end explains why IMD's 2026 outlook is not worse than it is — the positive IOD signal tempers what could have been a more severe deficit.

Monsoon–Inflation–Economic Growth Nexus

In a predominantly agrarian economy with incomplete irrigation coverage, monsoon performance directly transmits to macroeconomic variables. About 50% of India's net sown area is still rain-fed; a weak monsoon drives up food prices, suppresses rural consumption, widens the fiscal deficit (through higher food subsidy and relief spending), and forces RBI to navigate conflicting pressures of growth and inflation.

A 10% rainfall deficit historically correlates with a 40–60 basis point increase in CPI food inflation over the subsequent 6 months.
Vegetable and pulse prices are most sensitive; cereals less so due to buffer stock operations.
Hydropower generation falls during deficit monsoon years, raising electricity tariffs and industrial costs.
Rural demand — which drives 35–40% of FMCG sales and two-wheeler purchases — contracts meaningfully in drought years.
The fiscal cost of drought relief and MGNREGS escalation can add 0.2–0.4% of GDP to the central fiscal deficit.

Connection to this news: A monsoon 8% below LPA in 2026 arrives at a time when India is already managing energy-side inflation from the West Asia crisis — the dual supply shock to food and fuel raises stagflation risks and complicates RBI's monetary policy stance.

Key Facts & Data

IMD estimate: 92% of LPA (8% below); Skymet estimate: 94% of LPA (6% below)
LPA (1971–2020): 868.6 mm; 92% corresponds to ~799 mm
Deficient probability: 35% (historical baseline: 16%)
IMD Phase 2 forecast: expected late May 2026
IOD status: currently neutral, forecast to turn positive by monsoon end
Eurasian snow cover (Jan–Mar 2026): slightly below normal (historically positive for monsoon)
El Niño peak risk window: August–September 2026
Rain-fed agricultural area: ~50% of India's net sown area (~70 million hectares)