What is causing widespread rainfall across India?

For the first time this season, the southwest monsoon is active over a large geographical area of India. At least 80% of the country last week reported widespread rainfall, with heavy to very heavy spells lashing Assam, West Bengal, Uttar Pradesh, Uttarakhand, Gujarat, coastal Maharashtra and Karnataka, Kerala, and Lakshadweep.

- 

After remaining subdued during mid-June, the southwest monsoon got the much-required impetus towards June-end. The monsoon covered the entire country on July 2, six days ahead of its normal schedule. Delhi, Punjab, Uttarakhand, Uttar Pradesh, Himachal Pradesh, Rajasthan, and Jammu and Kashmir received the spell in early July.However, since the start of this month, there have been multiple favourable weather systems that have kept the monsoon either active or vigorous (with respect to rainfall events) over southern peninsular, east, northeast, and central India regions. There have been two main contributors to the enhanced rainfall. One is the continuous incoming of moisture-laden strong westerly winds from the Arabian Sea. The other is the position of the monsoon trough - a semi-permanent, low-pressure area extending between Pakistan and the Bay of Bengal during the monsoon season which usually oscillates between north and south within the season. Whenever it moves towards the south, as it has done in the present case, more rainfall can take place in central, eastern and peninsular India. When it shifts towards the north, the Himalayan foothills are likely to rece