Explained | Why India is experiencing one of the wettest Octobers in decades

October rains are not uncommon but scientists say delayed monsoon and development of low pressure areas have led to heavy rainfalls

A motorcyclist rides through heavy rain in New Delhi, Sunday. Credit: PTI Photo

While October rains are not uncommon, this year several parts of the country are seeing unprecedented rainfall. Places like Kerala and Uttarakhand have received downpour that led to loss of life and property. The national capital also saw high rainfall throughout the month.

Scientists told The Indian Express a combination of delayed monsoon and the development of low-pressure areas have led to heavy rainfalls in the country this month.

Here's a look at the reasons behind unprecedented rain in October in some states in many decades.

1. Transition Period:

October is the transition period when the southwest monsoon withdraws and allows passage for the northeast monsoon. The latter affects the southern peninsula on the eastern side.

2. Western disturbances:

Western disturbances interfere with local weather and cause either extreme snow or rainfall. Over the last week, Uttarakhand, Kashmir and Ladakh have reported the first snow of the season.

Also Read | Incessant rain claims 11 more lives in Uttarakhand; Nainital cut off from rest of state

3. Low-pressure systems:

Two low-pressure systems have formed over the Arabian Sea and Bay of Bengal. These have collectively triggered heavy rains over the Indian peninsula, specifically in Kerala, Tamil Nadu, Andhra Pradesh, Telangana, Delhi, Madhya Pradesh, Uttarakhand, Odisha and West Bengal.

4. Delayed monsoon withdrawal:

The southwestern monsoon usually withdraws by early October. This leads to thunder and localised rainfalls in India. However, while monsoon usually withdraws by September 17, this year the withdrawal was delayed to October 6.

It has withdrawn from the northern and eastern peninsula but it still persists over the southern peninsula.

By mid-October, monsoon winds reverse direction and flow from southwest to northeast. This year the onset of the northeast monsoon is expected around October 25.

As for Kerala, heavy rains were triggered by the low-pressure system from the Arabian Sea colliding with the one over north Andhra and southern Odisha. This interaction caused southwest winds which brought in rainfall.

A low-pressure system over central India is still active alongside a low-pressure system over Bengal and Odisha. This coupled with moist easterly winds from Bay of Bengal means that the country is going to see some rainy days going forward.

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