• Source:JND
Add as a preferred

Early Arrival of Monsoon 2025: The Southwest monsoon set in over the Indian state of Kerala on Saturday, eight days earlier than the usual date of June 1. The last time monsoon arrived in Kerala this early was in 2009 and 2001. The monsoon arrival marks the beginning of the four-month, June-September, southwest monsoon season over India, contributing more than 70 per cent to annual rainfall. There has been speculation around the factors that could have triggered the early onset.

Here are the probable reasons behind the early monsoon onset.

Several reasons, including the development of large-scale atmospheric and local factors, have contributed to the monsoon's arrival before the date. Contrary to the usual date, the monsoon arrived early over the south Andaman Sea and neighbourhood areas on May 13, instead of May 21.

1. The Madden-Julian Oscillation (MJO)

This complex ocean-atmospheric phenomenon contributes majorly to Indian monsoons and is considered the most important factor, as it originates in the India ocean. When a disturbance of clouds, wind and pressure moves eastward at a speed of 4-8 metres per second, the MJO wind bands can travel around the world within 30-60 days and impact weather conditions around the world heavily. If this activity happens around India, it can catalyse rainfall during the monsoon. 

2. Mascarena High

The India Meteorological Department (IMD) explains that a high-pressure area near the Mascarene Islands in the south Indian Ocean plays a significant role in India's monsoon rainfall. Changes in its intensity of this pressure influence heavy rainfall along India's west coast.

3. Vertical Transport of Heat And Moisture And Somali Jet 

When heat and moisture travel vertically, the activity is called convection. The increase in convection activity also contributes to the rainfall in India. According to a report by the Indian Express, the heat and moisture moved southward from Haryana last week and led to the rainfall in Delhi.  A low-level, inter-hemispheric cross-equatorial wind band originating near Mauritius and north Madagascar is called the Somali Jet. It reaches the Arabian Sea and the west Coast of India after crossing the African Coast in May. The stronger Somali Jet, the stronger monsoon winds in India. 

ALSO READ: 'Kaun Raat Ke Andhere Mein': Rajesh Kumar Mimics Bilawal Bhutto’s Viral Speech In Rosesh Sarabhai Style | Watch

4.  A low-pressure area develops in the Arabian Sea after the Sun moves towards the northern hemisphere. A low-pressure zone over Pakistan and nearby areas acted as a catalyst, drawing in moist air along the monsoon trough and boosting rainfall.

5.  The monsoon trough is an elongated low-pressure area extending from the heat low to the north Bay of Bengal.  When the trough swings north-south, it triggers rainfall during the June-September period in the core monsoon zone.

When Is Monsoon Declared

The monsoon is considered active if at least 60% of 14 southern meteorological stations (including Minicoy, Amini, Thiruvananthapuram, and others) record rainfall of 2.5 mm or more for two consecutive days. Along with this, the India Meteorological Department (IMD) relies on other inputs such as the blow of westerly winds from west to east, and the Earth absorbing and reflecting energy from the Sun, and the difference between these processes impacts the Earth’s temperature and atmosphere. The weather department declares monsoon arrival if all the said factors come to notice.  

The IMD attempts to declare the schedule for southwest monsoon onset any time after May 10.

Also In News