Massive dry air to enter Northwest, West India, force monsoon to pack its bags

The southwest monsoon could soon begin its retreat from large parts of India as a massive mass of dry air is likely to enter Northwest and West India after September 19-20, potentially stripping the region of the moisture needed to sustain monsoon rainfall.

The influx of dry air is expected to clear out much of the remaining atmospheric moisture over Northwest India. It could provide the push needed to initiate the monsoon withdrawal process.

The development comes as the monsoon enters its final phase over the country. Conditions are already becoming favourable for the withdrawal of the southwest monsoon from parts of West Rajasthan around September 19, marking the beginning of the seasonal transition.

However, the retreat may not progress smoothly across the rest of the country.

According to the forecast, an incoming low-pressure system (LPS) over central, eastern and other parts of India could temporarily interrupt the withdrawal process. The system is expected to keep moisture and rainfall activity alive over large parts of the country even as dry air begins taking over the northwest.

This could create a sharp contrast in weather conditions across India, with the northwest turning progressively drier while central and eastern regions continue to receive monsoon rainfall.

The monsoon withdrawal over Central and Eastern India may therefore be delayed until around September 30, according to the forecast. The retreat is expected to resume after the low-pressure system weakens and dissipates.

The interaction between the advancing dry air and the incoming low-pressure system will therefore be crucial in determining how quickly the monsoon can finally withdraw from the country.

Normally, as the monsoon retreats, large-scale atmospheric circulation begins changing, moisture availability decreases, and dry continental air starts replacing the humid monsoon air mass. The process begins over northwest India before gradually progressing towards central, eastern and southern parts of the country.

This year, however, the withdrawal could occur in stages, rather than as a clean, uninterrupted retreat.

For Northwest India, the arrival of dry air after September 19-20 could mark the first major step towards the end of the rainy season. But further south and east, the lingering low-pressure system could keep the monsoon active for several more days.

The result could be a late September tug-of-war between dry air pushing in from the northwest and moisture-rich weather systems holding on over the rest of India.