Monsoon at Kerala's doorstep but likely to miss June 1 onset

📌 Summary:

• IMD said southwest monsoon is likely to miss its 1 June onset over Kerala this year — normal onset date is 1 June with permissible deviation of ±7 days
• Conditions favourable for further advance over southern peninsula (Kerala, Tamil Nadu) in the coming 4-5 days; monsoon already over southwest/southeast Arabian Sea, Lakshadweep, Comorin, Bay of Bengal
• Onset dates in recent years: 2023 — 8 June; 2024 — 30 May (early); 2025 — 24 May (early)
• Andaman Sea onset 2026 — already realised on 16 May, nearly a week ahead of normal
• All-India southwest monsoon rainfall forecast: BELOW NORMAL — quantitatively 90% of Long Period Average (LPA) of 870 mm (1971-2020 base)

🎯 UPSC Relevance: GS1 — Climatology/monsoon dynamics; GS3 — Agriculture (kharif sowing, foodgrain output), water resources, disaster preparedness.

📝 Prelims Facts:

• Long Period Average (LPA) of southwest monsoon: 870 mm (1971-2020)
• IMD rainfall categories: Normal (96-104% of LPA); Below Normal (90-96%); Deficient (<90%); Above Normal (104-110%); Excess (>110%)
• Southwest monsoon = June-September; accounts for ~75% of India's annual rainfall
• Monsoon advances from Kerala northwards covering entire country by ~8 July; withdraws from NW India by 17 September
• Andaman Sea onset precedes Kerala onset by ~10-12 days

🔑 Key Term: Long Period Average (LPA) — Average rainfall recorded over a 50-year reference period; IMD uses 1971-2020 LPA of 870 mm for all-India southwest monsoon to grade each year's rainfall (Normal/Below Normal/Deficient etc.).