Monsoon likely to set in over Kerala around June 4: IMD

📌 Summary:

• India Meteorological Department (IMD) on June 2, 2026 revised its southwest monsoon onset forecast — now LIKELY around Thursday, June 4, 2026
• Originally, on May 15, IMD had predicted onset over Kerala on May 26 (with model error of plus/minus 4 days)
• June 4 OVERSHOOTS even the upper bound of that window (May 30)
• This is the FIRST TIME SINCE 2015 that IMD has failed to correctly call the monsoon's Kerala arrival
• In 2015 too, a May 30 forecast had given way to a June 5 actual onset
• IMD's operational onset forecast model has been ACCURATE every year from 2005 to 2025 except for that single 2015 lapse
• The southwest monsoon makes its first landfall on the Indian mainland over Kerala — the conventional start of India's rainy season
• A late onset has cascading effects: delays kharif sowing, affects reservoir levels, impacts rural demand

🎯 UPSC Relevance: GS1 — Climatology, monsoon phenomenon; GS3 — Agriculture, food security, climate change linkages.

📝 Prelims Facts:

• Normal monsoon onset over Kerala: June 1 (with a standard 4-day error window)
• 2026 expected onset: June 4 (overshoots upper bound)
• IMD operational onset forecast model accurate from 2005–2025 except for 2015
• IMD = India Meteorological Department; established 1875; HQ: New Delhi; under Ministry of Earth Sciences (MoES)
• The southwest monsoon contributes ~70-75% of India's annual rainfall
• Mission Mausam (recently launched) seeks to upgrade IMD forecasting capability

🔑 Key Term: Southwest Monsoon Onset — the seasonal arrival of monsoon rains over Kerala, marking the start of India's principal rainy season; declared by IMD using objective criteria including rainfall, wind patterns and outgoing longwave radiation (OLR).