Above Normal Rainfall Likely In September: Weather Office

The country received 24 per cent less than normal rainfall in August, a vast deviation from the IMD's predictions for the month, but latest forecasts say it is expected to be above normal in September.

Above normal rainfall to normal rainfall is likely over many parts of central India in September, India Meteorological Department (IMD) Director General Mrutunjay Mohapatra said Wednesday.

The IMD also "updated" the overall rainfall forecast for the season and it is now likely to be around the lower end of normal rainfall, he added.

This is for the third time that the monsoon forecast has been revised by the IMD. On April 16, the First Long Range Forecast for Southwest Monsoon said rainfall is expected to be 98 per cent of the Long Period Average (LPA) with an error of 5 per cent. The LPA of the season's rainfall over the country as a whole for the period 1961-2010 is 88 cm.

The IMD raised it to 101 per cent of the Long Period Average (LPA) with a model error of plus or minus 4 per cent in its Second Long Range Forecast on June 1.

"Monthly rainfall over the country as a whole during September is most likely to be above normal (over 110 per cent of the Long Period Average)," the IMD said.

Mr Mohapatra said normal to below rainfall is expected over north and northeast India, and southern parts of south India.

The monsoon deficit now stands at nine per cent and this is expected to come down due to good rainfall during September, Mr Mohapatra said.

July had recorded seven per cent less rainfall, while June had recorded 10 per cent more, according to the meteorological department.

The country received 24 per cent less than normal rainfall in August. 

Of the four meteorological divisions of the IMD, the central India division received 39 per cent less. The division consists of a large swathe of area from Maharashtra, Gujarat, Goa, Madhya Pradesh, Chhattisgarh and Odisha.

The deficiency in the northwest India division that comprises northern Indian states was 30 per cent.

The deficiency was 10 per cent in the south peninsula whereas the east and northeast division received 2 per cent more rainfall than the normal.

The IMD had predicted that the rainfall activity was expected to be normal during August.

When asked about the reasons behind the forecast going off-the mark, Mr Mohapatra said negative Indian Ocean Dipole conditions which are unfavourable for Indian monsoon prevailed during the month.

Mostly August rainfall deficiencies are associated with El Nino/negative IOD events. It was observed in nine out of 15 years since 1965, he said.

But a negative IOD condition is not the only factor that affects the monsoon, he noted. El Nino is associated with the heating of the Pacific waters while a negative IOD is linked to the heating of the Indian Ocean waters.

Also, there was an absence of monsoon depression. Normally two monsoon depressions form in the month of August, Mr Mohapatra said.

He added that only two low pressure areas were formed as against four (August 16-18 and August 28-30.)

Mr Mohapatra said the latest global model forecasts indicate that prevailing ENSO (El Nino) conditions are likely to continue over the equatorial Pacific Ocean, and the negative Indian Ocean Dipole conditions over the Indian Ocean region during September.

However, sea surface temperatures (SST) over the central and east equatorial Pacific Ocean are showing signs of cooling and there is an increased possibility of re-emergence of the La Nina conditions at the end of the monsoon season or thereafter, the IMD chief said.

"As SST conditions over the Pacific and Indian Oceans are known to have strong influence on the Indian monsoon, the IMD is carefully monitoring the evolution of sea surface conditions over these ocean basins," Mr Mohapatra said.

When asked about the withdrawal of Southwest Monsoon from northwest India, he said normal rainfall activity is likely over the region for the first two weeks of September.

Southwest Monsoon starts retreating from northwest India from September 17. But he pointed to the trend of delayed retreat of monsoon from northwest India.