The monsoon is bracing for a productive interaction with an approaching western disturbance over the North-West India, which could translate into heavy to very heavy rainfall and even extremely heavy rainfall over the region this weekend.

The monsoon is known to interact with periodic western disturbances, low-pressure band of waves coming in from across the border. This is the first time during this season that such an interaction would happen.

System interaction

The monsoon rain for North-West India is otherwise dependent on the East-to-West movement of low-pressure areas from the Bay of Bengal and exactly oppposite (West-to-East) movement of western disturbances from the Pakistan border.

The odd western disturbance had been moving in, but had not obliged the monsoon with the typical ‘dip’ over North-West, which occasions the interaction with the monsoon system.

The dip would take the disturbance southward over Rajasthan, Haryana, Delhi, Uttar Pradesh and Bihar. Heavy precipitation is indicated for along the hills of North-West India,

On Wednesday, the ‘low’ from the Bay was embedded into the monsoon trough, the atmospheric highway to North-West India, and was located over North-East Madhya Pradesh and South-East Uttar Pradesh.

Extended outlook

It has already caused widespread rain over Madhya Pradesh on Wednesday, and promises the same for East Rajasthan for two more days. Further onward movement of the ‘low’ would cause it to run into the incoming western disturbance from Friday.

An extended three-day outlook from early next week predicted fairly widespread to widespread rainfall for East and North-East India; scattered to fairly widespread rainfall with isolated heavy falls over the hills and adjoining plains of North-West India.

The heavy precipitation due to the interaction between the monsoon system and the western disturbance will begin to lift from August 20 (Wednesday next) while scattered rainfall is forecast for the rest of the country until then.

The 24 hours ending on Wednesday morning saw exceptional showers over Bolangir in Odisha (55 cm); Chalakkudy in Kerala (17 cm); Rewa in Madhya Pradesh (15 cm); Gokarna in Coastal Karnataka (14 cm); and Brahmapuri in Odisha (13 cm).

Weak phase likely

Low-level convergence of monsoon westerlies from the Arabian Sea caused heavy to very heavy rain over parts of North Kerala on Wednesday. But the intensity of rainfall over Kerala is expected to reduce from Thursday, the IMD said.

This would happen with the possibility of the heavy rain belt regime migrating to East and North-East India and along the foothills of the Himalayas over North-West India .

This would bring about another weak phase — when rains decrease over large parts of the country — which is inevitable after a hyper-active session of the monsoon till date in August.

This is also the phase when thunderstorms break out along the East Coast, including Tamil Nadu, Andhra Pradesh, Odisha, and the North-East, fetching their due share during the season.

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