IMD Forecasts Early Southwest Monsoon 2025 — Kerala to Receive Rains 5 Days Ahead of Schedule

Detailed Summary

On May 21, 2025, the India Meteorological Department (IMD) announced that conditions are favourable for the onset of the Southwest Monsoon over Kerala within 3 to 4 days, i.e., five days ahead of its usual date of June 1. IMD Scientist Naresh Kumar, speaking exclusively to Akashvani News, confirmed this forecast and added that the monsoon is likely to advance into parts of Bengal and the Northeast shortly afterwards. The monsoon eventually made landfall in Kerala on May 24, 2025 — eight days ahead of schedule — the earliest onset since 2009 (when it had arrived on May 23rd).

IMD also predicted that the 2025 monsoon season would be above normal, quantitatively expected to reach 105% of the Long Period Average (LPA). This was the second consecutive year that IMD predicted an above-normal monsoon.

Maharashtra, Kerala, Goa, and Coastal Karnataka were experiencing heavy rainfall as of May 21, 2025, with similar conditions forecast for the next five to six days. IMD issued a Red Alert for heavy to very heavy rainfall over these regions.

Historical Background

The Southwest Monsoon is India's primary rainy season, bringing over 70–80% of the country's annual rainfall during June–September. It originates over the Arabian Sea and Bay of Bengal, and its onset over Kerala — typically on June 1 — marks the official beginning of the Indian monsoon season. The onset date is closely monitored by farmers, governments, and economists as it determines the Kharif cropping calendar.

The IMD has been predicting the monsoon onset date using statistical models since 2005, with only one incorrect prediction (2015) in 20 years. Past onset dates include: May 30 (2024), June 8 (2023), May 29 (2022), June 3 (2021), June 1 (2020). The 1990 arrival was on May 19, the earliest on record.

Tamil Nadu Relevance

An early and above-normal Southwest Monsoon has significant benefits for Tamil Nadu:

• Early recharge of major reservoirs such as Mettur Dam (Stanley Reservoir) on the Cauvery River, which feeds delta irrigation.
• Benefits Kharif crops including paddy, groundnut, cotton, and pulses sown in Tamil Nadu.
• The Northern Limit of Monsoon on May 24, 2025 was passing through Dharmapuri and Chennai in Tamil Nadu — showing rapid monsoon penetration.
• Tamil Nadu receives Northeast Monsoon (October–December) as its primary rainfall source, but early Southwest Monsoon also benefits western Tamil Nadu, the Nilgiris, and Ghat areas.

Why Important for TNPSC

The monsoon system is a core topic for TNPSC Group 1, Group 2 Geography and Environment sections. Key concepts include origin of monsoon, LPA, onset dates, Kharif crops, and the role of Bay of Bengal branch vs Arabian Sea branch of the monsoon.

Key Highlights

• IMD forecast: Southwest Monsoon to arrive over Kerala 5 days early.
• May 21, 2025 forecast: Onset expected within 3–4 days.
• Actual onset: May 24, 2025 — 8 days ahead of schedule.
• Earliest onset since 2009 (May 23rd) and before that 1990 (May 19th).
• 2025 monsoon forecast: Above normal — 105% of LPA.
• Heavy rainfall continuing in Maharashtra, Goa, Kerala, Coastal Karnataka.
• Northern Limit of Monsoon passed through Dharmapuri and Chennai in Tamil Nadu.

Important Facts Table

Important Terms and Definitions

• Long Period Average (LPA) — The average monsoon rainfall calculated over a 50-year period (1971–2020). Current LPA is approximately 87 cm for India as a whole.
• Above Normal Monsoon — Rainfall greater than 104% of LPA.
• Kharif Crops — Crops sown at the beginning of monsoon season (June–July) and harvested by September–October. Examples: paddy, maize, cotton, groundnut, sugarcane.
• Red Alert (IMD) — Warning of extremely heavy rainfall (more than 20 cm in 24 hours); action required immediately.
• MJO (Madden-Julian Oscillation) — An eastward-moving tropical disturbance that enhances rainfall. It played a key role in the 2025 early monsoon advance.

Exam-Oriented Notes

• Normal SW Monsoon onset over Kerala: June 1.
• 2025 onset: May 24 — 8 days early — earliest since 2009.
• LPA = Long Period Average (1971–2020 base period currently).
• Above normal = more than 104% of LPA.
• Kharif crops benefit from early monsoon.
• Tamil Nadu mainly gets Northeast Monsoon; but early SW Monsoon benefits western TN and Ghat regions.
• IMD headquarters: New Delhi.

MCQs

MCQ 1

Q: The normal onset date of the Southwest Monsoon over Kerala is:

• A) May 15
• B) June 1
• C) June 15
• D) July 1

Answer: B) June 1

Explanation: The normal onset of the Southwest Monsoon over Kerala is June 1, with a standard deviation of approximately seven days. In 2025, it arrived on May 24 — eight days ahead of schedule — the earliest since 2009.

MCQ 2

Q: What does LPA stand for in the context of IMD monsoon forecasts?

• A) Local Precipitation Average
• B) Long Period Average
• C) Lowest Precipitation Amount
• D) Land Pressure Average

Answer: B) Long Period Average

Explanation: LPA stands for Long Period Average, which is the average rainfall over a 50-year base period used by IMD as a benchmark for classifying monsoon seasons as deficient, normal, above-normal, or excess.

MCQ 3

Q: Which branch of the Indian monsoon primarily benefits Tamil Nadu?

• A) Southwest Monsoon — Arabian Sea Branch
• B) Southwest Monsoon — Bay of Bengal Branch
• C) Northeast Monsoon
• D) Western Disturbances

Answer: C) Northeast Monsoon

Explanation: Tamil Nadu primarily receives rainfall from the Northeast Monsoon (October–December), unlike most of India which depends on the Southwest Monsoon (June–September). This is why Tamil Nadu experiences its main rainy season in October–December while rest of India receives peak rain during June–September.