The monsoon has further advanced into more parts of Rajasthan, apart from covering remaining parts of Uttar Pradesh and Himachal Pradesh, entire Delhi, and some parts of Haryana and most parts of Punjab a day later on Thursday, mostly ahead of time.

But the overall rain surplus has receded to 22 per cent as the rainfall remained largely weak over Central India.

The northern limit of the monsoon linked Nagaur, Alwar, Delhi, Karnal and Firozepur across Rajasthan, Delhi, Haryana and Punjab. A helpful trough (a seasonal elongated corridor of low pressure area) ran down from Central Pakistan to Bihar across North-West Rajasthan, Haryana and Uttar Pradesh.

Seasonal trough in view

Ideally, the trough aligns itself along a track that originates over West Rajasthan, stretches to the South-East and cuts through parts of Central India and the Gangetic Plains before dipping into the North Bay of Bengal. Low-pressure areas breeding in the Bay wheel along this trough into East India and Central India before careening into the North-West, raining all the way across.

But India Meteorological Department (IMD) indicated that the trough (the monsoon trough) had not developed in an ideal manner, and was in a truncated form running in from North-West Rajasthan across the plains over land into Bihar. It also added that the trough may move to the North, instead of dipping in the Bay to nestle along the foothills of the Himalayas.

This phase is identified with less over large parts of the country. Exceptions are the West Coast, where a fresh monsoon pulse is active over Kerala and adjoining Karnataka, and parts of the East Coast, including Odisha, Coastal Andhra Pradesh and Tamil Nadu. The movement of the trough to the foothills would bring very heavy and flooding rains to North-East and adjoining East India during the next 3-4 days, the IMD said.

Rains for West Coast, East India

Widespread rainfall with isolated heavy to very heavy rainfall has been forecast to continue over this region. Isolated extremely heavy rainfall is also likely over Bihar, Assam and Meghalaya from Thursday to Saturday and over Arunachal Pradesh and the hills of Bengal and Sikkim on Friday and Saturday.

Fairly widespread to widespread rainfall activity with isolated heavy to very heavy falls is likely over East Uttar Pradesh until Sunday. Isolated heavy rainfall was forecast over the remaining parts of the hills of North-West (Jammu & Kashmir, Himachal Pradesh and Uttarakhand) and adjoining plains on Thursday.

As for the South, fairly widespread to widespread rainfall with isolated heavy to very heavy rainfall will continue for next four days. Isolated extremely heavy rainfall is likely over Kerala on Friday and Saturday.

The Climate Prediction Centre of the US sees fresh rain bands invading the West Coast from the first of July, the rainiest of the four monsoon months. Significantly, it also sees the North Bay witnessing a spurt in rain activity alongside. The Arabian Sea and the Bay humming in unison is the best thing to happen for the monsoon. The Myanmar national forecaster, the closest, alludes to the formation of a low in the Bay in its backyard to coincide with this phase.

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