The Hindu Business Line : Monsoon makes its way to Kolkata

THE southwest monsoon brought Kolkata into the rain belt on Monday, a fortnight behind schedule. However, it whizzed past Hyderabad on its eastward course, prolonging the city's agonising wait.

The northern limit of the monsoon passed through Veraval, Mumbai, Pune, Sholapur, Kurnool, Kakinada, Kolkata, Malda and Siliguri on a day when the Arabian Sea arm of the system strengthened further, bringing heavy rain along the west coast.

India Meteorological Department (IMD) is scheduled to announce a comprehensive update on the monsoon performance in the first week of July, said Dr M. Rajeevan, Director, Forecasting, Pune.

Speaking from a long-range forecaster's view, he said that for all its horrific consequences, the prevailing heat wave would help bring down the pressure levels over the northern plains and set up the monsoon `heat low' in the region.

"What we now lack is a properly organised heat low, a significantly vital component of the monsoon system," Dr Rajeevan told Business Line.

The heat low is usually formed in the desert where there are few clouds. The main heat low is over Pakistan, and across the international border into Rajasthan. Viewed from the planetary angle, the `Indian monsoon heat low' extends from northern hemisphere Africa to southern Asia.

When fully evolved, mainland India's monsoon trough anchors to one side of this heat low, about 450 km south of the Himalayas. Dr Akhilesh Gupta, Director of the National Centre for Medium Range Weather Forecasting (NCMRWF), said the heat low would help strengthen the pressure gradient and fire up the Arabian Sea arm of the monsoon.

This summer heat low system, extending from Somalia across southeast Arabia to northwest India, is known to be the most extensive and intense on Earth.

But according to information from the Pakistan Meteorological Department, Dr Gupta said, that the heat had just started building up in those parts in anticipation of the low. There are positive signs about the build-up there, and across the border into Rajasthan.

An ideally formed pressure gradient will link Thiruvananthapuram (around 1008 millibars) in the south, to Rajasthan (992-993 millibars) in the north.

The present barometer reading over Rajasthan is around 996 millibars.

In its update, the NCMRWF said that the monsoon had further advanced over entire central Arabian Sea, parts of north Arabian Sea, southern most parts of Saurastra and Kutch, some more parts of northwest Bay of Bengal, parts of Gangetic West Bengal and all of sub-Himalayan West Bengal.

Prediction suggests that the monsoon may progress further and cover some more parts of Saurastra and Kutch, the south Gujarat region, more parts of Madhya Maharashtra, parts of Marathwada, some more areas of Telangana, entire coastal Andhra Pradesh, parts of Orissa, all of West Bengal, parts of East Bihar and Jharkhand, during the next five days.

Improvement in the heat wave condition is expected over interior Orissa, Bihar, Jharkhand, Chhattisgarh and coastal Andhra Pradesh during the next 3-4 days.

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