India Meteorological Department (IMD) declared the early monsoon onset, eight days ahead of its normal date schedule.

• Southwest monsoon normally sets in over Kerala around 1st June. The last such early onset occurred in 2009.

Factors for early onset of Monsoon

• Madden-Julian Oscillation (MJO): An atmosphere-ocean coupled phenomenon in the tropics that enhanced cloud and wind patterns, favouring early rainfall.
• Mascarene High: High-pressure system near Mascarene Islands (in south Indian Ocean) intensified monsoon flow towards India.
• Convection: An increased convective activity i.e. the vertical transport of heat and moisture in the atmosphere, also brings rainfall.
• Somali jet: A low-level, cross-equatorial wind band originating near Mauritius and north Madagascar that strengthened monsoon currents over the Arabian Sea.
• Heat-low: Intense heat low (pressure departure is below normal) along the continent surrounding the Arabian Sea creates a shallow low-pressure zone which acts as a suction device, pulling moist air along the monsoon trough and enhancing rainfall over India.
• Monsoon trough: It is an elongated low-pressure area extending from the heat low to the North Bay of Bengal. Its southward shift leads to active monsoon conditions across India.