Southwest monsoon expected to onset over Kerala around June 4: IMD

📌 Summary:

• India Meteorological Department (IMD) on June 2, 2026 said southwest monsoon onset over Kerala is most likely on June 4, 2026 — close to the normal onset date of June 1 (standard deviation ±7 days)
• Conditions favourable for further advance into Kerala, Tamil Nadu, Lakshadweep, more parts of the Arabian Sea and the Bay of Bengal on June 4
• This year's monsoon onset over the Andaman Sea (the first stage of advance) occurred on May 16, 2026 — broadly on time; progress since has been timely
• Heavy to very heavy rainfall (60-200 mm in 24 hours) forecast for Wednesday and Thursday across Kerala
• "Orange" alert (be prepared to take action) issued for 8 Kerala districts: Thiruvananthapuram, Kollam, Pathanamthitta, Alappuzha, Kottayam, Ernakulam, Idukki, Thrissur

🎯 UPSC Relevance: GS1 Geography (Indian monsoon, climatology), GS3 Disaster Management (heavy rainfall warnings, district-level alert framework), GS3 Agriculture (kharif sowing dependence on monsoon timing).

📝 Prelims Facts:

• Normal monsoon onset over Kerala: June 1 (±7 days standard deviation)
• 2026 onset over Andaman Sea: May 16
• 2026 monsoon onset over Kerala: June 4 (forecast)
• IMD alert colour codes: Green (no action), Yellow (watch), Orange (be prepared), Red (take action)
• Definition of "heavy" rainfall: 64.5-115.5 mm/day; "very heavy": 115.6-204.4 mm/day; "extremely heavy": >204.4 mm/day

🔑 Key Term: Monsoon Onset over Kerala (MoK) — IMD declares MoK only after specific criteria are met: (i) ≥60% of 14 designated stations record ≥2.5 mm rainfall for 2 consecutive days, (ii) westerly winds at certain depth & speed, (iii) outgoing longwave radiation (OLR) thresholds — making MoK a scientifically defined event, not a calendar event.