May 18: The monsoon, which advanced earlier than usual over the Bay of Bengal, may now temporarily weaken and make slower progress because Laila is deserting it, a senior meteorologist said today.

The monsoon advanced over parts of southwest and southeast Bay of Bengal today, two days ahead of the normal date, sharing energy with a cyclonic storm Laila that was located about 1,250km southwest of Calcutta this morning.

But till this evening, Calcutta was not in the path of the storm — which has formed a week before the first anniversary of cyclone Aila that ravaged Bengal on May 25, 2009.

The cyclone will now detach from the monsoon,” said Damodar Pai, a director at the India Meteorological Department (IMD), Pune. “Further progress of the monsoon will then depend on how the cyclone behaves,” Pai told The Telegraph.

“Laila is stationed about 570km east-southeast of Chennai and 690km southeast of Visakhapatnam,” Gokul Chandra Debnath, the director of the Regional Meteorological Centre in Calcutta’s Alipore, said this evening.

“We are tracking Laila round the clock. As of tonight, it’s much closer to Andhra than us. It’s moving north-westwards, so it does not look likely to reach us. The picture would be clearer tomorrrow,” said Debnath.

Laila appeared heading west-northwestward and is expected to cross the Andhra coast within the next two days, Pai said. As long as it is over the ocean, the cyclone is expected to pick up more moisture — and energy.

When the monsoon and Laila decouple, the moisture will get distributed between the two, but the intensity of the cyclonic storm will draw more moisture, he said.

“This may cause a slowdown in the progress of the monsoon — until the monsoon regains energy,” Pai said. Scientists expect Laila to lose energy after it moves over land. “The faster this cyclone decays, the better it is for the monsoon.”

A computer simulation of the cyclonic storm suggests that it is likely to intensify further and move in a northwest direction over the next 72 hours towards Andhra, close to Machilipatnam.

“Gale force wind with speed reaching 65-75km per hour is likely to commence along and off the Andhra coast from tonight. It may increase subsequently as the (storm) system moves closer to the coast,” said an IMD official.

Heavy to very heavy rain could occur over north Tamil Nadu and coastal Andhra in the next 48 hours, the official said. “Sea conditions will be rough along and off the Andhra coast and very rough along and off the north Tamil Nadu coast,” the official added. Fishermen have been warned against venturing into the sea.

The energy build-up in the monsoon flow is expected to accelerate once Laila decays. The anticipated temporary slowdown in its progress may not cause any change in the date of onset over Kerala, predicted to be May 30, a scientist said.

The monsoon line had advanced over the Andaman and Nicobar islands and the southwestern part of the Bay of Bengal on Monday and further moved today over parts of the east-central Bay of Bengal.

Last year, Aila had sucked out moisture, causing a delay in the progress of the monsoon.