A Lull, Not a Withdrawal
Just as the rainy season enters its final month, the southwest monsoon has gone quiet over large parts of India, particularly in the southern peninsula. The India Meteorological Department (IMD) noted on September 7 that rainfall activity is likely to
remain subdued in this region for about a week. However, this is a temporary pause, not the end of the season. While some areas are dry, the monsoon remains active elsewhere, influenced by a low-pressure area over central Uttar Pradesh and the persistent monsoon trough. Now, meteorologists are watching the Bay of Bengal, where the next major player is taking shape.
What Is This 'Bay of Bengal System'?
The upcoming rain is expected to be triggered by a cyclonic circulation. Think of this as a large-scale swirling of winds in the atmosphere. The IMD's extended-range forecast indicates this circulation is likely to form over the west-central and adjoining northwest Bay of Bengal. Under its influence, a low-pressure area is expected to form in the same region. A low-pressure area is like an atmospheric vacuum cleaner; it pulls in moist air from its surroundings. Because this system is forming over the warm sea, it will draw in a huge amount of moisture. This moisture-laden air then moves over land, rises, cools, and condenses to form rain clouds, leading to significant rainfall.
The Monsoon's Rain-Making Engine
The Bay of Bengal is a veritable factory for monsoon weather systems. Its warm sea surface temperatures and high humidity provide the perfect fuel for creating low-pressure areas, depressions, and even cyclones. These systems are often guided westwards by the monsoon trough, an elongated low-pressure belt that extends from northwest India to the bay. When the eastern end of this trough dips southwards over the bay, it creates favourable conditions for these rain-bearing systems to form and intensify. These systems then typically travel across central and northern India, delivering widespread, heavy rainfall along their path.
Where and When to Expect Rain
While the system is still forming, the IMD has already forecast its likely impact. This new system is expected to cause an increase in rainfall over east and adjoining peninsular India during the first half of the week of September 10-16. Specifically, fairly widespread rain is expected over Chhattisgarh from September 8 to 12. The Vidarbha region can expect rain from September 10 to 12, with Odisha also seeing increased rainfall during the same period. While peninsular India might stay relatively dry for a little longer, this Bay of Bengal system signals that the weather pattern is set to become active once again.
Context of a Below-Normal Season
This incoming spell of rain arrives against the backdrop of a challenging monsoon season. After the hottest August since 1901, the IMD has forecast that rainfall in September is likely to be below normal for the country as a whole. The cumulative monsoon rainfall as of early September was already in deficit, largely due to the influence of El Niño conditions, which tend to suppress monsoon rainfall. However, the forecast also noted that parts of northwest, northeast, and east-central India could still receive normal to above-normal rainfall in September. Spells of rain generated by systems like the one brewing in the Bay of Bengal are crucial for making up shortfalls and supporting agriculture in the final phase of the season.
