Intense rainfall to continue over sub-Himalayan WB, Bihar and UP: IMD

Several parts of the west coast, including Mumbai and Konkan, and sub-Himalayan West Bengal were pounded by exceptionally heavy rainfall on Tuesday and Wednesday, triggering severe urban flooding and landslides in the hills as the monsoon nears the start of its withdrawal phase.

The India Meteorological Department (IMD) predicted very heavy rainfall in parts of north-east India, sub-Himalayan West Bengal, Konkan. Bihar and eastern Uttar Pradesh (UP) for the next two-three days.

For example, in Mumbai, the Bandra Kurla Complex (BKC) recorded 37 centimetres (cm) of rainfall on Tuesday night; Dharavi (36 cm); Panvel (31 cm); and Santacruz (29 cm), triggering flooding in the city and disrupting traffic.

In West Bengal, Jalpaiguri and Bagdogra recorded 18 cm of rainfall each. IMD takes into account a 24-hour rainfall data.

However, according to IMD scientists most of the rainfall was recorded within 12 hours – between Tuesday night and Wednesday early morning. Updated rain data for Wednesday will be available later on Thursday.

“There is a convergence of strong moist southerly and south-westerly winds from the Bay of Bengal over the north-east and adjoining eastern India. This is the reason behind the region receiving heavy rainfall. There is a low-pressure system lying over central parts of western Madhya Pradesh (MP) which is likely to re-curve towards UP in the next couple of days and bring in widespread rainfall,” said K Sathi Devi, head of the IMD’s national weather forecasting centre.

There are no indications of the commencement of the monsoon’s withdrawal from north-western India because of moisture incursion into the region, Devi said.

IMD is not seeing any parameters of monsoon withdrawal being met until September 28, according to a statement by the department on Wednesday.

The monsoon season will officially end on September 30.

Rainfall should stop completely; water vapour should reduce and an anticyclonic wind pattern should establish itself before the monsoon’s withdrawal is officially announced, according to Devi.

A low-pressure area is lying over central parts of western MP. It is likely to become less marked by Thursday. However, the cyclonic circulation, which is associated with it, is likely to re-curve north-eastwards to Bihar across UP over the next three days.

Convergence of strong, moist southerly and south-westerly winds from the Bay of Bengal over the north-east and adjoining eastern India is very likely until Saturday (September 26).

A trough, which means a low-pressure area, is running from north-east UP to northern Maharashtra.

Heavy-to-very heavy rainfall will continue over sub-Himalayan West Bengal, Sikkim, parts of Konkan, UP and Bihar until Saturday, according to IMD.

The normal date for commencement of monsoon withdrawal from north-west India is September 17 and for complete withdrawal from the country is October 15, as per the new monsoon onset and withdrawal dates issued by the IMD in April.

Until last year, the normal date for commencement of withdrawal of monsoon was September 1 and October 15 for a complete withdrawal. The new onset dates are based on monsoon data from 1961 to 2019 and withdrawal dates are based on data from 1971 to 2019 analysed by scientists in IMD, Pune.

In 2019, the monsoon had started withdrawing only on October 9 against the normal date of September 1 and prolonged rainfall had brought a deluge to parts of Maharashtra, Kerala and Bihar in August when rains usually reduce.

The monsoon had withdrawn completely only by October 17.

In September, rains are 0.6% deficient across the country. Since June 1, the country has recorded 8.1% excess rainfall, according to the IMD.