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.
Essential criteria to declare early onset of monsoon as per IMD Guidelines
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