Vigorous and relentless monsoon rainfall has put this month on course to be the wettest September India has seen in 102 years and lifted the June-September season’s rain to 9% above normal, barely a percentage point short of excess monsoon rainfall.

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With a day left in the month, all-India average rainfall in September stands at 247.1mm — 48% above normal and the third highest in

’s records since 1901. By Monday, the month’s rainfall is likely to go past 1983’s figure (255.8mm), as red alerts for very heavy rain have been issued for

and Bihar. If that happens, this will be the wettest September in India in over a century, behind only 1917 (285.6mm), when the highest rainfall for the month since 1901 was recorded.

This year’s monsoon, which began with a delayed onset and a 33% rain deficit in June, will officially end on Monday with the country recording the highest rainfall for the four-month period in 25 years. The all-India average seasonal rainfall stands at 956.1mm, 9% higher than the normal of 877mm till Sunday.

The monsoon’s retreat is still not in sight. “There are still no signs of withdrawal for at least the next four-five days,” said Mrutyunjay Mohapatra, director general of meteorology at IMD.

Monsoon has been active over the country almost without a break for over two months now. Cumulative rainfall in August and September so far is the highest the country has witnessed for these two months in 31 years. By Monday, August-September rainfall could end up as the highest in 58 years (since 1961) and fourth highest since 1901, as per IMD’s records.

Such has been the monsoon’s vigour in the second half of the season that September has recorded just two days of below normal rains across the country. In August, that figure was 10, still low by normal standards.

IMD said there were three reasons for the monsoon deluge since August. “El Nino conditions over the

, which suppress the monsoon, receded in July. At the same time, conditions in the

became favourable for monsoon with the

turning positive. The third factor was the development of a series of low pressure systems in the Bay of Bengal. Although the number of such systems wasn’t unusually high, some of these caused heavy rains for a long time by persisting over the central Indian region,” said Mohapatra.

The top IMD official particularly pointed to one low pressure system that continued to remain active for over 10 days, mainly hovering over

and east

.

This pattern of rainfall, seen since the third week of July, soaked central India in particular. The region went from being 20% monsoon deficient to over 28% rain surplus by the end of the season. The turnaround was even more dramatic in south India, which was reeling under a monsoon deficit of nearly 30% by July 19, with drought conditions in many districts. By September-end, the region was 16% rain surplus for the season.

While the monsoon was adequate in northwest India, which currently has a slight deficit of 3%, the region clearly missed out on the rain bounty. Haryana, Delhi and east

in particular will end the season with high deficits.