Why has October been so wet?

The monsoon has passed, yet rain continues to pour in some parts of the country. For the past few days, Delhi, Kerala, Madhya Pradesh, and Uttarakhand have seen very heavy rainfall, resulting in the loss of life and property in some areas. The city of Delhi has just seen one of its wettest 24-hour periods in decades.

According to scientists, a combination of circumstances, including a delayed monsoon and the emergence of low-pressure zones in different locations, has resulted in severe rainfall occurrences in multiple locations.

It’s not unusual for it to rain in October. October is a month of transition, as the southwest monsoon retreats and gets replaced by the northeast monsoon, which primarily impacts southern peninsular India on the eastern side.

Western disturbances, which begin to have a substantial impact on local weather over India’s far north, frequently result in rain or snowfall. The first snowfall of the season has been observed in Ladakh, Kashmir’s higher regions, and Uttarakhand since late last week.

Two low-pressure systems were active last week, one over the Arabian Sea and the other over the Bay of Bengal. Severe weather events are triggering in Kerala, Tamil Nadu, Andhra Pradesh, Telangana, Delhi, Madhya Pradesh, Uttarakhand, Odisha, and West Bengal as a result of these events.

Monsoon withdrawal delayed

By early October, the four-month southwest monsoon season is usually over. It creates thunderstorms and localized heavy rains during the withdrawal phase.

This year though, the withdrawal started on October 6 instead of September 17, as is customary. The monsoon has left the Western, Northern, Central, and Eastern India areas entirely dry. However, it continues to be active over the southern peninsula. Kerala, Tamil Nadu, Telangana, Karnataka, and Andhra Pradesh have all received significant rainfall in the last ten days.

Until Monday, the monsoon had not passed over Manipur, Mizoram, Tripura, few parts of West Bengal and Odisha, and the entire southern peninsular India.

“Good rainfall has remained over Odisha, the Northeast, and south India due to a delay in the southwest monsoon retreat,” said Mrutyunjay Mohapatra, director general, India Meteorological Department (IMD).

By mid-October, the monsoon winds have usually reversed their flow direction from southwest to northeast.

The northeast monsoon is on its way, according to D Sivanand Pai, head of Climate Research and Services at IMD in Pune.

Conditions for the northeast monsoon to begin this year are likely to develop around October 25.

Extremely heavy rains

At least two low-pressure systems remained active along the east and west coastlines, as well as over central India, for the majority of last week, bringing rain to significant sections of the country.

Between Sunday and Monday, Delhi received 87.9mm (over a 24-hour period), making it the fourth wettest October day in the city since 1901. October has also been the fourth wettest month thus far. So far this month, it has gotten 94.6 mm of rain, second only to the 238.2 mm received in 1954, 236.2 mm in 1956, and 186.9 mm received in the full Octobers of 1910.

Similarly, Balasore in Odisha received 210mm in a single day, marking only the second time in a decade that this has happened this month.

While the northeast monsoon brings heavy rains to Tamil Nadu between October and December, Coimbatore (110mm) experienced the wettest October day in a decade, even before the northeast monsoon arrived.

The Western Ghats, northeast, and central India are noted for receiving a lot of rain. However, in recent years, it has been observed that strong bouts over a short period are becoming more common.

“As a result of climate change, extreme weather events are becoming more frequent throughout the year. However, the formation of low-pressure systems can be ascribed to these specific incidences of heavy to extremely severe rains that we are seeing right now,” Mohapatra added.

“Whenever there is a low-pressure system, it results in heavy to very heavy rainfall activity, depending on its strength. Furthermore, when a low-pressure system combines with a western disturbance, it causes more severe rainfall,” he explained.

Kerala has seen heavy rains

Between October 15 and 17, a low-pressure system emerged in the east-central Arabian Sea and migrated and stayed over Kerala.

A low-pressure system formed along the north coast of Andhra Pradesh and southern Odisha at the same time. The interplay between them boosted southwest winds, which brought heavy rains to Kerala’s central and southern regions during the weekend.

The 24-hour rainfall was over 200 mm in various areas of the Idukki, Ernakulam, Kollam, and Kottayam districts. Water run-off generated landslides and mudslides in many of these districts, which are steep and densely forested.

There will be rainy days ahead

The low-pressure system that hit Kerala has now dissipated. However, similar pressure is currently active over central India, resulting in good rainfall in northern India this week.

Heavy rain is expected in Western Uttar Pradesh, Uttarakhand, and Himachal Pradesh on Tuesday, prompting the IMD to issue a red alert for these areas.

Another low-pressure system is active, and its interaction with the moist easterly winds from the Bay of Bengal is predicted to produce heavy rain to West Bengal, Odisha, Sikkim, and Bihar through Wednesday. On Tuesday, the greatest effect in terms of exceptionally heavy rain (more than 204 mm in 24 hours) is expected over parts of West Bengal and Sikkim.

Furthermore, till Wednesday, strong southeasterly winds from the Bay of Bengal are likely to bring heavy rain to Arunachal Pradesh, Assam, and Meghalaya.

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