Rains set to bridge north-south divide

Rith Basu, TT,  June 9: The monsoon is likely to arrive in Calcutta around the same time as north Bengal for the first time in years under the impact of a low-pressure area over the Bay of Bengal.

The Met department said the rain-bearing winds were likely to arrive in the city in two-three days.

The city has been experiencing pre-monsoon showers over the past few days but they have failed to bring any relief from the seasonal swelter - a fact borne out by CESC's power consumption figures.

Calcutta has between June 1 and 7 consumed 268 million units of power - the highest during the period over the past few years. The spurt is being attributed to long use of air-conditioners.

"The consumption from June 1 to 7 this year was 12.42 per cent higher than the corresponding period last year," a power utility official said.

The maximum temperature today was 36.1 degrees Celsius, a notch above normal. The temperature and a high minimum relative humidity - 53 per cent - pushed up the RealFeel (calculated by weather portal AccuWeather.com) to 48 degrees Celsius.

Metro answers your queries about the south-west monsoon and how different are this year's winds compared with previous years.

What's unique about this year's monsoon?

Generally, the eastern arm of the monsoon reaches north Bengal before Calcutta and the rest of south Bengal. But the low-pressure area over the Bay, which formed today, is likely to turn the curvature of the northern limit of monsoon roundish (see chart). That's why the monsoon will arrive in most of north Bengal and eastern parts of south Bengal simultaneously, a rarity in meteorological history.

Where are the monsoon winds stuck now?

The eastern arm of the northern limit is stuck over Bangladesh and the north eastern states. The other arm, moving south to north, has covered half of Andhra Pradesh and Karnataka.

Based on what factors meteorologists declare that the monsoon has arrived at a particular place?

There are three such factors

• The south-westerly wind must blow up to a height of 2km above the surface.

• The rainfall must be fairly widespread, covering at least 75 per cent of the region. Which means of the 60 rain gauges across Calcutta, at least 45 should record showers.

• The presence of a favourable weather system in the vicinity. The formation of a low-pressure area on the Bay has fulfilled the criterion.

Why has the progress of the monsoon been delayed since its arrival in Kerala?

The monsoon reached Kerala on June 1, two days ahead of schedule. It reached the North-east the same day, four days ahead of schedule. The early arrival was attributed to cyclone Mora on the Bay.

But after that, a well-marked low-pressure area on the Arabian Sea, which later made landfall in Oman, had prevented further advance of the winds. Now that the formation has dissipated, conditions are ripe for the monsoon to renew its flow.

Which factors influence the flow of the south-west monsoon?

The strength of the winds around the Mascarene Plateau, a submarine plateau in the southern hemisphere where they generate, and local factors such as a low-pressure belt over the Bay of Bengal.

The weather department expects the conditions to remain conducive to the arrival of the monsoon in north Bengal and Calcutta in two-three days.