Monsoon downpours focus on northern India as river flooding threatens the North East

By Courtney Spamer, AccuWeather meteorologist

By Kristina Pydynowski, AccuWeather senior meteorologist

September 1,2018, 10:46:56 AM EDT

The greatest risk for flooding from monsoon downpours will focus on north-central India into this week, while the country's North East region is facing river flooding following heavy rain that inundated China.

China alerted India that the swollen Yarlung Tsangpo River could flood more communities in Arunachal Pradesh as runoff from recent torrential rain in Tibet drains downstream.

The Yarlung Tsangpo River is known as the Siang River in Arunachal Pradesh and the Brahmaputra River in Assam.

Those living in low-lying ares along the river in both Arunachal Pradesh and Assam are being put on alert for potential flooding, according to the Times of India. These residents should prepare for possible evacuations.

In this handout photo provided by the Indian Air Force, villagers are airlifted during a rescue operation at an isolated island on the Siang River in the northeastern Indian state of Arunachal Pradesh, Friday, Aug. 31, 2018. The air force used a helicopter to rescue 19 people who became stuck on an island in the Siang when the tiny spit of land became inaccessible by boats. (Indian Air Force via AP)

Flooding along the river has already prompted at least 19 people to be airliftedfrom a small island in Arunachal Pradesh. More than 200 others were rescued from Assam's Dhemaji district as over 1,000 families in the Mebo area of Arunachal Pradesh have been affected.

Runoff from monsoon downpours targeting North East India daily through next week, the most numerous of which will occur over the higher terrain, may further raise the river’s level and put more communities along the river’s edge at risk.

The river has already risen in Arunachal Pradesh with unusually high waves being reported.

Avoid venturing into the swollen river for fishing, swimming and other activities. Where the river overflows its banks to flood roads and communities, residents are reminded never to attempt to drive or walk through flood waters. It takes only 150 mm (6 inches) of fast-flowing water to knock down an adult and 300 mm (a foot) to carry away a small vehicle.

Monsoon downpours are also raising concern for flooding back to north-central India.

Once again, cities such as Indore and Kanpur will be impacted by these daily downpours through the middle of next week.

Unlike the previous week, the periods of heavy rain will expand to affect other cities as well.

A weak low will enhance the rainfall around the city of New Delhi, for not only the weekend but into the new week as well.

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The other main difference will be the presence of daily downpours in eastern India, including the states of Bihar, Jharkhand and West Bengal.

"While localized flooding may occur around the National Capital Region and eastern India, a slow-moving storm will bring the heaviest rain and greatest risk of flooding to western Uttar Pradesh and northern Madhya Pradesh," AccuWeather Senior Meteorologist Adam Douty said.

The storm can bring a total rainfall amount of 100-200 mm (4-8 inches) through Wednesday, with an AccuWeather Local StormMax™ of 300 mm (12 inches).

"This heaviest rain may focus on areas in between New Delhi and Lucknow with Agra and Gwalior at risk," Douty said.

Rainfall amounts of this magnitude are capable of producing life-threatening flooding, as well as mudslides in the mountainous areas. Rounds of downpours can also lead to widespread travel disruptions.

Meanwhile, largely dry weather is expected for far northwestern India.

By late week, the India Meteorological Department could declare the monsoon withdrawn from these areas, said AccuWeather Senior Meteorologist Jason Nicholls.

This is the first step in the withdrawal of the monsoonal rain from India, which on average begins in the first weeks of September. This process continues throughout the autumn, with monsoonal moisture slowly retreating southward across the country into early December.