Driest August, but near normal rainfall likely in September, says IMD

Low rainfall has meant that the average maximum temperature recorded in August – 32.09 degrees Celsius – was the highest since 1901, a degree above  the normal of 31.09 degrees Celsius. The average minimum temperature of 24.7 degrees Celsius in August was the second highest for the month since 1901.

Bihar, eastern Uttar Pradesh, Jharkhand, Chhattisgarh, Gangetic West Bengal, Kerala, parts of Karnataka, and Maharashtra recorded deficient rainfall in August, while rainfall in Himachal Pradesh and Uttarakhand was in the normal range.

Rainfall over the country in September is likely to be normal, between 91 per cent and 109 per cent of the long period average of 167.9 mm. While normal to above normal rainfall is expected over Northeast India, east India, foothills of the Himalayas, and parts of east-central and south peninsular India, below normal rainfall is likely over the rest of the country, IMD said in its forecast.

From June 1 to August 31, the country recorded 629.7 mm of rainfall, against the normal of 700.7 mm.

IMD Director General Mrutyunjay Mohapatra pointed to El Nino conditions, a warming of equatorial Pacific Ocean waters that is associated with suppression of rainfall, as a major factor for deficit rain in August.

“El Nino was one of the most important factors to have caused deficient rainfall activity in August. In addition to that, there are many other factors – the Madden Julian Oscillation was unfavourable, low-pressure systems did not form (there were only nine low pressure system days against a normal of around 16.3 days in August), and the Indian Ocean Dipole (IOD) was neutral,” he said.

The Madden Julian Oscillation refers to an eastward moving system of clouds and wind along the equator, which can influence rainfall depending on whether it is in an active or weak phase.

While weak to moderate El Nino conditions are prevailing over the Pacific Ocean, it is expected to strengthen and extend into the early part of next year, Mohapatra said.

An IOD that is now positive, which is marked by warming over the western Indian Ocean and cooling over the eastern Indian Ocean, could help counter the impact of El Nino conditions in September.

“The expectation is that a positive Indian Ocean Dipole will, to some extent, counter the adverse impact of El Nino conditions, which is why the forecast for September is for normal rainfall,” Mohapatra said, adding that other factors that could bring normal rainfall in September are the formation of low-pressure systems, and favourable Madden Julian Oscillation.

“There will be a change in the trend of rainfall activity in September when compared to August… the break monsoon situation which is prevailing now is going to end, and from September 2 onwards we can expect revival of the monsoon. The activity will start over the eastern parts of the country and peninsular India, and then gradually over the other parts of the country,” he said.