Using an independent system of weather modelling, scientists at the Indian Institute of Science have determined that the onset of the monsoon will be later than expected.

Scientists at the Institute’s Divecha Centre for Climate Change said that the findings were made after creating a weather model as part of the Centre’s research into how atmospheric pressure, including pressure at surface, makes it possible to forecast the onset of the monsoon a few weeks in advance.

The precise date as revealed by the statistical model will stay a secret until the India Meteorological Department makes its announcement, said Professor J Srinivasan, distinguished scientist at the Centre, and associate professor Arindam Chakraborty, who built the model.

Expounding how he had determined that the monsoon would be delayed, Chakraborty explained that he had fed his model data from the India Meteorological Department and the United States’ National Centre for Environmental Prediction (NCEP), while considering three parameters: surface pressure, water vapour and the position of the Africa-Asia Upper Level Jetstream, which races over the subcontinent at an altitude 8-10 km and at a speed of 25 metres per second.

“If the onset is early, it is generally indicated by lower than normal surface pressure over west Asia in the month of May. A lower pressure there intensifies the low-level westerly winds over Arabian Sea and brings more moisture over Indian land, bringing early onset. This year, the surface pressure over west Asia is higher than normal, along with other parameters, indicating a delayed onset,” he added.

He clarified that the monsoon onset isochrones, having originated in the South China Sea, is already on its way to India. “The onset isochrones travels through the various Southeast Asian regions, till it enters the Bay of Bengal and then Kerala.”

According to Dr G S Srinivasa Reddy of Karnataka State Natural Disaster Monitoring Centre, the Meteorological department will probably make its announcement next week.