The South-West monsoon, a key factor for India’s agricultural production, has set in over Kerala. However, the onset of monsoon, which accounts for about 74 per cent of the country’s total rainfall, has been delayed by a week. Private forecaster Skymet said it agreed with IMD on the onset of monsoon.

India Meteorological Department (IMD) said the monsoon, which was stalled from June 2, advanced into the remaining parts of the south Arabian Sea and some parts of the central Arabian Sea, the entire Lakshadweep area, most parts of Kerala, most parts of south Tamil Nadu, remaining parts of Comorin area, Gulf of Mannar and some more parts of southwest, central and northeast Bay of Bengal on Thursday. 

Conditions are favourable for further advancement of the monsoon into some more parts of central Arabian Sea, remaining parts of Kerala, some more parts of Tamil Nadu, some parts of Karnataka and some more parts of southwest, Central and northeast Bay of Bengal and some parts of north-eastern States during next 48 hours, the weather bureau said.

60% below normal in 1st week

India gets 868.6 mm (average in last 50 years) rainfall during June-September monsoon season, against its annual normal precipitation of 1176.9 mm. Normally, monsoon arrives in Kerala on June 1 , covers the entire country by July 15 and completely retreats by October 15.

Due to the delayed arrival, Kerala has been deficient by 61 per cent and Tamil Nadu by 25 per cent since June 1 whereas the pan-India rainfall until June 8 was 60 per cent below normal. Except one district, all other places in Kerala have received deficient rainfall during June 1-8. However, as the monsoon has advanced bringing continuous rains in many districts, the deficiency is likely to reduce.

Monsoon onset over the Kerala coast last year was three days ahead of normal, but missed the IMD’s forecast date of May 27. It covered the entire country six days ahead of normal. The monsoon rainfall was 106 per cent of normal of 87 cm in 2022. The IMD has predicted a ‘normal’ monsoon for this year, which may be 96 per cent of long period average (LPA). However, private weather forecaster Skymet sees it at 94 per cent of normal.

Storage levels

According to IMD, there is a good chance of emergence of moderate El Niño during monsoon season, but its impact on disrupting rainfall in the country may be neutralised with a likely positive Indian Ocean Dipole (IOD). Monsoon rainfall between 96-104 per cent of long-period average (LPA) of 868.6 mm is known as ‘normal’ and between 90-95 per cent of the LPA is considered as ‘below normal’.

Some atmospheric indicators such as the Southern Oscillation Index (SOI) have shifted towards El Niño thresholds, but wind, cloud and broad-scale pressure patterns indicate the Pacific Ocean and atmosphere are yet to reinforce each other, as occurs during El Niño events.

The South Asian Climate Outlook Forum (SASCOF) expects the monsoon to deliver below normal rainfall over some areas in the North-West, Central and North-East of the South Asia region, while above normal rainfall is likely over the North and North-West, as well as parts of East and South-East. 

Data from the Central Water Commission showed the storage level in the 146 major reservoirs in the country was 28 per cent of the total live storage capacity of 178.185 billion cubic metres (BCM). This was six percentage points lower than the same period a year ago.