Why India's Southwest Monsoon Onset Is Delayed: Key Weather Conditions Unmet

Top Summary

• What happened: The official declaration of the southwest monsoon onset is stalled as key wind and rainfall criteria remain unfulfilled.
• Why it matters: Proper onset tracking is essential for forecasting, but an active cyclonic circulation is currently disrupting critical wind patterns.
• What changes: Forecasters must observe persistent westerly winds and specific rainfall amounts across 14 stations before confirming the monsoon.
• Who is affected: Agricultural sectors and populations across Kerala, Karnataka, and Lakshadweep awaiting the seasonal rainfall.

The Critical Hurdles Stalling the Monsoon

The official arrival of the southwest monsoon in India remains in limbo. Although the initial prediction date of May 26 has passed, meteorological conditions have not met the required thresholds.

To officially declare the monsoon's onset, weather scientists monitor two crucial parameters. These include establishing sustained westerly winds and recording specific rainfall levels across designated regional stations.

While the normal onset date is June 1, meteorologists note that it has a standard deviation of seven days. Currently, both primary conditions remain unfulfilled.

Wind Patterns Disrupted by Cyclonic Circulation

The first key factor is the setup of stable, moisture-laden westerly winds traveling from Madagascar to India. However, an upper air cyclonic circulation over the southeast Arabian Sea near the Lakshadweep area has blocked this progress.

This atmospheric circulation is causing the wind direction to shift constantly. An IMD official explained the situation:

"The westerly winds have to be persistent and well-marked. However, the prevailing upper air cyclonic circulation is causing frequent shifts in the directions, with winds alternating between westerly, easterly and other directions. This makes it difficult to ascertain whether a stable westerly wind has been established or not. It will be clear once the circulation pattern is over."

Rainfall Criteria Across 14 Stations Unmet

The second condition for the official declaration relies on specific rainfall distribution. According to IMD guidelines, at least eight to nine out of 14 designated stations must record 2.5mm of rain or more for two consecutive days after May 10.

Presently, approximately 60% of these 14 stations have failed to meet this rainfall benchmark. These critical monitoring stations are spread across three regions:

• Lakshadweep: Amini and Minicoy
• Kerala: Thiruvananthapuram, Punalur, Kollam, Kottayam, Alappuzha, Kochi, Vellanikkara, Kozhikode, Thalassery, Kannur, and Kudlu in Kasaragod
• Karnataka: Mangaluru

The Impact of Climate Change on Forecasting

Historically, rainfall was the sole factor used to declare the southwest monsoon onset. Westerly wind patterns were later integrated into the criteria to improve accuracy using satellite technology.

However, changing environmental factors may require a revision of these standards. An IMD official remarked on the evolving situation:

"Around 60% of the 14 stations are yet to record 2.5mm rainfall and above consecutively for two days... With climate change, we will have to change the criteria for weather forecasts."

What to Watch Next

Meteorologists will closely monitor the upper air cyclonic circulation over the Arabian Sea to see when it dissipates. Observing the 14 designated rain gauge stations for consecutive rainy days will be critical in the coming days. The official monsoon onset will only be declared once wind patterns stabilize and rainfall targets are met.