The southwest monsoon’s arrival over Kerala has been delayed once again, highlighting the complex scientific criteria that govern its official declaration. While several parts of the state have already witnessed substantial rainfall, the India Meteorological Department (IMD) has revised the expected onset date to around June 4, three days later than the normal onset date of June 1.
The delay comes after an earlier forecast issued by the IMD on May 15 had projected an early onset around May 26. However, the weather system failed to develop as anticipated, forcing forecasters to push back the timeline.
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Why has the monsoon been delayed?
According to News 18, rainfall alone is not enough for the official declaration of the southwest monsoon. The IMD follows a set of scientific benchmarks that must occur simultaneously before the monsoon can be formally announced.
Fresh weather model assessments indicate that the strong upper-level winds required to support a fully established monsoon circulation may only develop after June 5 or 6. Until then, the weather system remains incomplete despite the presence of rain-bearing clouds over Kerala.
Widespread and sustained rainfall
The first requirement is widespread rainfall across a network of designated weather stations in Kerala.
According to News 18, the IMD analyses rainfall data from multiple locations and requires a majority of these stations to record prescribed rainfall levels for two consecutive days. This ensures that the rainfall is part of a structured monsoon system rather than isolated pre-monsoon showers or thunderstorms.
Although parts of Kerala have experienced heavy rain, the required consistency across monitoring stations has not yet been achieved.
Strong westerly winds over the Arabian Sea
The second benchmark involves wind patterns.
According to News 18, the southwest monsoon is driven by strong moisture-laden westerly winds that blow from the Arabian Sea towards the Indian subcontinent. These winds transport enormous amounts of moisture and help sustain widespread rainfall.
Meteorologists say the current westerly flow remains weaker than expected, limiting the monsoon’s ability to establish itself fully over Kerala.
Deep cloud formation and low OLR values
The third condition relates to cloud development and atmospheric convection.
According to News 18, weather scientists monitor satellite imagery and a parameter known as Outgoing Longwave Radiation (OLR), which helps assess cloud thickness and convective activity. Lower OLR values generally indicate dense cloud cover and stronger monsoon conditions.
At present, cloud formations over Kerala have not consistently shown the organised, large-scale structure typically associated with a mature southwest monsoon.
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Why does the delay matter?
According to the southwest monsoon, it is critical for India’s agriculture, water resources and overall economy. According to News 18, Kerala serves as the official gateway for the monsoon’s arrival into the country, making its onset closely watched by farmers, policymakers and weather experts alike.
While a delay of a few days is not unusual, this year’s repeated revisions have drawn attention because the IMD had initially predicted an earlier-than-normal onset. The eventual arrival around June 4 would still be within the range of normal variability, but it underscores how sensitive monsoon forecasting remains to evolving atmospheric conditions.
