Rainfall during August and September, the second half of the four-month rainfall season, is likely to be on the higher side of normal, the India Meteorological Department (IMD) said on Monday. In another forecast for August, IMD Director General Mrutunjay Mohapatra said monsoon is also likely to be normal in the month.
West Madhya Pradesh and adjoining Rajasthan, some parts of interior Maharashtra, Jammu and Kashmir, Ladakh, some parts of Punjab and Himachal Pradesh are likely to receive below normal rainfall in August, Mohapatra said.
Karnataka, Tamil Nadu, Telangana, Rayalaseema region of Andhra Pradesh, Konkan and Goa, central Maharashtra, south Gujarat, northeastern states, Bihar are likely to receive above-normal rainfall during the month, he added.
“The 2021 August to September rainfall averaged over the country as a whole is most likely to be normal (95 to 105 per cent of Long Period Average or LPA) with a tendency to be on the positive side of the normal," Mohapatra said at an online briefing.
The LPA of the August to September period rainfall over the country as a whole for the years 1961-2010 is 428.3 mm. Every year, the IMD issues forecast for the second half of the Southwest Monsoon, for August and September.
The spatial distribution suggests that below normal to normal rainfall is likely over many parts of the north, east and northeast parts of the country. Normal to above normal rainfall is most likely to be experienced over most parts of peninsular India and adjacent central India, the IMD said.
The IMD has also started issuing a month-wise forecast for the four-month rainfall season from this year. For August, it said, “Rainfall averaged over the country as a whole is most likely to be normal (94 to 106 per cent of LPA)."
The LPA of the August rainfall over the country as a whole for the period 1961-2010 is 258.1 mm. The spatial distribution suggests that below normal to normal rainfall is likely over many areas of central India and some areas over north India.
“Normal to above normal rainfall is most likely over most parts of peninsular India and northeast India," he added.
Mohapatra added that currently, the Sea Surface Temperatures (SSTs) and the atmospheric conditions over the equatorial Pacific Ocean indicate neutral ENSO (El Nino) conditions. The SSTs are one of the major factors that influence the Indian monsoon.
The SSTs over central and east equatorial Pacific Ocean are showing cooling tendency. The latest forecasts suggest that ENSO neutral conditions are likely to continue during the remaining part of the monsoon season and increased possibility of re-emergence of the La Nina conditions in the end of the monsoon season or thereafter.
La Nina is associated with the cooling of the Pacific Ocean waters, while El Nino is linked to its heating. In addition to ENSO conditions over the Pacific, other factors such as the Indian Ocean SSTs also influence the Indian monsoon. Currently, the negative Indian Ocean Dipole (IOD) conditions are prevailing over the equatorial Indian Ocean.
Forecasts indicate that negative IOD conditions are likely to continue during the remaining part of the monsoon season. A negative IOD is associated with the heating of the Indian Ocean waters, while a positive IOD is linked to its cooling. Positive IOD conditions are conducive for a good rainfall season.
Mohapatra said it has been observed that if October, November and December have La Nina conditions, then it helps in cyclogenesis (development or strengthening of cyclonic circulation in atmosphere) over the Bay of Bengal. The Southwest Monsoon arrived over Kerala on June 3, two days after its normal schedule. But it very rapidly covered the east, west, south and parts of north India by June 19, except for parts of west Rajasthan, Haryana, Punjab and Delhi.
But after that, it entered into a phase that witnessed a break. It started reviving from July 8. The Southwest Monsoon reached Delhi on July 13 after a delay of 16 days and covered the entire country the same day. June received 10 per cent more rainfall than normal. Of the four-month rainfall season, July and August receive the maximum precipitation.
This year, July recorded a rainfall deficit of seven per cent. The deficit was 25 per cent in the east and northeast India division of the IMD whereas the south peninsula received 27 per cent more rainfall than the normal. The northwest India division, which covers the northern states, and the central India division which encompasses the central Indian, west Indian states and Odisha, have registered a deficiency of 7 per cent.
Overall, the country has received one per cent less rainfall than normal from June 1 to July 31. The deficit was 13 per cent in the east and northeast subdivisions of the IMD. The northwest India division recorded a 2 per cent deficit.
The south peninsula division which covers the southern states received 17 per cent more rainfall while the central India division that comprises west and central India recorded one per cent more rainfall than the normal.