Understanding the Monsoon 'Break'
First, it is important to understand that this slowdown is a normal, if sometimes worrying, feature of the four-month monsoon season. Meteorologists refer to it as a 'break' period, characterised by a significant reduction in rainfall activity, especially
over the Indian peninsula. These breaks can last for several days and often lead to a rise in daytime temperatures and drier conditions. According to the India Meteorological Department (IMD), rainfall activity is expected to remain subdued over peninsular India for about a week from September 7, but this is a temporary lull, not the official withdrawal of the monsoon. As of September 7, the country's cumulative rainfall deficit for the season stood at 14% below the long-period average.
The Primary Cause: A Shift in the Monsoon Trough
The main driver behind a monsoon break is the behaviour of the monsoon trough. This is an elongated low-pressure area that typically extends from northwest India across the plains to the Bay of Bengal. For widespread rain to occur, this trough needs to be active and positioned over the heart of the country. During a break phase, the trough often shifts northward, closer to the foothills of the Himalayas. This shift starves the rest of the country of the moisture and atmospheric instability needed to produce widespread rain, leading to the dry spell currently being experienced across central and southern India.
Trigger 1: A New System in the Bay of Bengal
The most powerful and common trigger for a monsoon revival is the formation of a low-pressure area or a cyclonic circulation over the Bay of Bengal. These weather systems act like engines, pulling the monsoon trough southward from the Himalayan foothills back to its normal position over the plains. This re-establishes the flow of moisture-laden winds from the sea to the land, revitalising rainfall across eastern, central, and subsequently, other parts of India. Forecasters are constantly monitoring the Bay for signs of such a system developing, as it holds the primary key to ending the current break and initiating the next spell of widespread, active monsoon rains.
Trigger 2: The Madden-Julian Oscillation (MJO)
Another significant, albeit more complex, factor is the Madden-Julian Oscillation (MJO). The MJO is a massive, eastward-moving pulse of clouds, rainfall, winds, and pressure that circles the tropical and subtropical regions of the globe every 30 to 60 days. It has different phases, and its location can either enhance or suppress rainfall over the Indian subcontinent. When the MJO is in a favourable phase and its active convection is over the Indian Ocean, it can significantly boost monsoon activity and trigger heavy rainfall. Conversely, when it is in an unfavourable phase, it can contribute to a break in the monsoon. The movement of the MJO into a favourable position for India is another key development that meteorologists watch for to predict a revival of rain.
What the Forecast Says Now
While peninsular India remains largely dry, the monsoon is not entirely absent. As of September 8, the IMD has forecast fairly widespread rain over several states. Chhattisgarh, Vidarbha, and Odisha are expected to see renewed rainfall between September 8 and 12. Heavy rainfall is also predicted for parts of Uttar Pradesh and Uttarakhand through September 13. However, for large parts of the north, northwest, and south, a more definitive revival awaits the formation of a strong new weather system. Models suggest that atmospheric conditions may become more favourable for a widespread revival around the second half of September.
