A monsoon is the seasonal wind shift that causes heavy rainfall in South Asia. More precisely, it is a large-scale seasonal reversal in atmospheric circulation accompanied by a major change in precipitation.
During the South Asian summer monsoon, winds generally blow from the southwest toward the Indian subcontinent after crossing the Arabian Sea and Bay of Bengal. These moisture-rich winds rise over mountain ranges such as the Western Ghats and Himalayas, cool, and release intense rainfall. The southwest monsoon normally arrives in India around June and withdraws between September and October.
The summer rains are crucial for agriculture, reservoirs, ecosystems, and economies across India, Bangladesh, Nepal, Pakistan, Sri Lanka, and nearby regions. South Asia’s summer monsoon supplies roughly 70–90% of annual precipitation in many areas, though totals vary widely by location.
A monsoon is not simply a sudden rainstorm. El Niño can influence monsoon strength, the jet stream helps shape its timing and circulation, and trade winds contribute to its broader mechanics—but none is the name of the seasonal rainfall system itself.