Key Highlights
- The Andaman and Nicobar archipelago records the earliest monsoon rainfall in the nation, typically around 22 May.
- Thiruvananthapuram, Kerala’s capital, is the first mainland city to experience the southwest monsoon, usually on 1 June.
- Kerala’s location at the peninsula’s tip and the barrier effect of the Western Ghats accelerate the onset of rains.
- The monsoon advances north‑eastward, reaching Mumbai, Kolkata and Delhi in successive weeks, and covers all of India by mid‑July.
- IMD declares monsoon onset only after specific rainfall thresholds and wind conditions are satisfied at designated stations.
Detailed Insights
Each summer, soaring temperatures across the subcontinent generate a nationwide anticipation for the monsoon. While the general public wonders where the rains first touch Indian soil, meteorologists distinguish between two milestones: the absolute first landfall and the first mainland city to register sustained precipitation.
When the Indian Ocean’s moisture‑laden breezes encounter the Andaman and Nicobar Islands, they often begin to condense as early as 22 May, making the islands the earliest point of contact for the southwest monsoon. Excluding the islands, the capital of Kerala—Thiruvananthapuram—receives the first continuous showers on or about 1 June, marking the official start of the season for the Indian mainland.
Kerala’s advantage stems from two geographic factors. First, its position at the southwestern extremity of the peninsula places it directly in the path of prevailing winds from the Arabian Sea. Second, the Western Ghats rise sharply inland, forcing moist air to ascend, cool, and release its latent heat as rain. This orographic uplift creates a concentrated zone of precipitation that serves as the monsoon’s gateway into the subcontinent.
After breaking over Kerala, the monsoon system migrates northward and eastward, following a fairly predictable sequence. Coastal Karnataka and Goa experience rains between 5–10 June, followed closely by Mumbai around 11 June. Kolkata receives its share between 10–15 June, while Delhi typically waits until the last week of June. By mid‑July, the entire nation—including the arid zones of Rajasthan—lies under the monsoon’s influence.
According to the India Meteorological Department (IMD), the 2026 season arrived early on the islands (18 May) and was expected to reach Kerala ahead of its historical benchmark. The department quantifies the season’s vigor using the Long‑Period Average (LPA); for 2026, rainfall projections hover around 92 % of the LPA, indicating a slightly below‑normal but not drought‑inducing season.
IMD’s formal declaration of monsoon onset relies on three scientific criteria: at least 60 % of pre‑selected stations must record ≥2.5 mm of rain for two consecutive days, accompanied by characteristic wind shifts and supportive atmospheric patterns. Only when these thresholds are collectively satisfied does the agency announce the official start of the southwest monsoon.
The monsoon’s significance cannot be overstated: it delivers roughly 70 % of India’s annual precipitation, underpins the agricultural calendar, and influences rural incomes and national economic growth. While the conventional onset date for Kerala is 1 June, inter‑annual variability can advance or delay this event, altering the six‑week trajectory needed for the rains to traverse from the southern tip to north‑western India.