Southwest Monsoon 2026 Reaches Kerala Three Days Late: How IMD Tracks Its Arrival

The southwest monsoon, the rain-bearing wind system that supplies most of India's yearly water, reached the Kerala coast on June 4, 2026. This was three days behind the normal onset date of June 1, and well past the date the weather office had earlier predicted. On May 15, the India Meteorological Department (IMD) had forecast that the monsoon would arrive on May 26, with a margin of give-or-take four days. Since the rain came on June 4, it missed even the outer edge of that window. This is the first time since 2015 that the forecast slipped beyond its own error margin, after a long run of accurate calls.

The IMD does not declare the monsoon's arrival casually. It waits until strict scientific conditions are met. After May 10, at least 60 percent of 14 chosen weather stations across Kerala and the nearby coast must record 2.5 millimetres or more of rain on two days in a row. At the same time, the moist westerly winds blowing in from the sea must reach a depth of about 4.5 kilometres above sea level and a speed of 20 to 25 knots, and there must be enough thick rain-cloud (called convective cloudiness) over the southeast Arabian Sea. These tests are designed to avoid a false alarm, since pre-monsoon showers can sometimes look like the real thing.

To watch the clouds form and move, the IMD relies on pictures sent by the INSAT series of weather satellites, such as INSAT-3DS, which sit high above the Earth and photograph the cloud cover continuously. One useful measure these satellites provide is cloud-top temperature: very cold cloud tops usually mean tall, towering storm clouds that can bring heavy rain. By studying these images on the IMD's public satellite portal, scientists and ordinary citizens can follow how the monsoon storms build up kilometres above the ground, not just the rain that finally falls. This satellite tracking, combined with rainfall and wind readings, is what allows the formal onset to be announced.

The 2026 onset comes under the shadow of a strengthening El Nino. El Nino is an unusual warming of the central and eastern Pacific Ocean that tends to weaken the Indian monsoon. The World Meteorological Organisation has put the chance of El Nino conditions developing at about 80 percent for July and August, the heart of the monsoon and the most important months for kharif (summer) sowing. The IMD has already forecast a below-normal season at about 90 percent of the long-period average. A weak monsoon would mean less water in reservoirs, slower recharge of groundwater, and trouble for farming, since more than half of India's cropped area depends directly on rain rather than irrigation.

Forecasters, however, caution against panic over the late start. History shows that the onset date has little link to how much rain the full season finally delivers. The monsoon has begun early and still failed, and begun late and still recovered. The warning example is 2015, the last year the onset forecast was missed: that monsoon also reached Kerala late and ended at just 86 percent of the average, a deficient year worsened by El Nino. For exam aspirants, the episode is a reminder that the monsoon's behaviour is shaped by ocean-atmosphere links, that the IMD uses precise rainfall, wind and satellite criteria to declare onset, and that the rain-fed nature of Indian agriculture makes a normal monsoon vital for the economy.