The normal date for the arrival of the monsoon in Bengal is June 10.

The initial rains occurs in North Bengal and gradually it spreads to the rest of Bengal, including the fertile Gangetic plain.

This year the monsoon has already arrived in the southern states of Kerala and Karnataka. The moistureladen winds twist towards the western part of the country leading to a heavy rainfall in Maharashtra.

"Heavy showers result in accumulation of water in Maharashtra," said Sen.

"The delay in the onset of monsoon is being noticed for the past five years which is badly affecting the economic condition of an agro-based state like Bengal," said Goutom Sen of Environmental Science department in Jadavpur University.

Regarding the thunderstorm which resulted in the death of five people in Murshidabad district, Bose said that it was the result of pre-monsoon effects. It is the result of a trough formed 1 km above the main sea level along east Uttar Pradesh, Jharkhand, Gangetic plain and North Bay. This trough, on maturation, is likely to create occasional rain in Bengal. But heavy shower is likely to occur in Orissa, said the director.

The delay in the onset of the monsoon cannot be solely associated with increase in pollution, think both Bose and Sen.