System is robust, could envelop parts of Karnataka too over next few days, says IMD

After some initial hiccups, the much awaited southwest monsoon raced ahead and set in over Kerala on Sunday — three days before the normal date of June 1.

The system set in over most parts of Kerala and covered most of the south of the Arabian Sea and some parts of Tamil Nadu, the south of the Bay of Bengal and the south of the Andaman Sea, the Indian Meteorological Department (IMD) said in a bulletin.

Conditions were favourable for further advance of the system, it said. In the next two to three days, it could cover all of Kerala, more parts of Tamil Nadu, the Arabian Sea, the south Bay of Bengal and the Andaman Sea.

A senior meteorologist at the IMD said the system was robust and some parts of Karnataka too could be covered over the next two to three days.

As of Sunday evening, the northern limit of the system had passed through Amindivi in Lakshadweep, Kozhikode in Kerala, Kodaikanal in Tamil Nadu and Nancowry in the Nicobar Islands.

The development sets at rest apprehensions that arose after the system failed to keep its date with the Andaman Sea region, which it normally covered by May 20 before moving on over Kerala around June 1.

In a release issued on May 13, the Department said the monsoon could set in over Kerala on May 31 with a model error of plus or minus four days.

In its annual pre-monsoon forecast for the four-month season issued earlier on April 19, the IMD had stated that rainfall during the season was “most likely” to be normal this year, at 98 per cent of the long period average (LPA), with a model error of plus or minus five per cent.

In a note issued along with the forecast, the IMD said models showed there was a 53 per cent probability for the rainfall to be between 96 per cent and 104 per cent of the LPA [normal], a 10 per cent probability for it to be between 104 per cent and 110 per cent of the LPA [above normal], and 1 per cent probability for it to be above 110 per cent of the LPA [excess].

On the downside, there was a 30 per cent probability for it to be between 90 per cent and 96 per cent of LPA [below normal] and a 6 per cent probability for it to be below 90 per cent of LPA [deficient].

This forecast is, however, not final, and will be updated around the last week of June, when new data emerges.

Most international models monitoring El Niño and La Niña climatic phenomena have indicated, among other things, that sea surface temperatures over the equatorial Pacific were warming up. Consequently, La Niña conditions, which could, otherwise, have been beneficial for the monsoon, have weakened and have reached El Niño Southern Oscillation condition.

According to recent forecasts, by international models for the June-August season, there was a very good chance that the neutral condition would continue: a probability of 57 per cent for the continuance of neutral condition, against a 22 per cent probability for the re-emergence of La Niña conditions and a 22 per cent probability for the development of El Niño conditions.

Long-term forecasts for El Niño-La Niña, however, are fraught with uncertainty. The phenomena may well unfold differently from the present forecast.

IMD officials emphasised that the Department would keep a close watch on the phenomena to ensure that the country was well prepared in case of any major changes.

The IMD, they said, would also closely monitor the developments relating to the Indian Ocean Dipole (IOD), which relates to anomalies in the sea surface temperatures between the eastern and western parts of the Indian Ocean.

At present, international models are forecasting that a negative IOD could develop and that it could happen in the last part of the monsoon. As a result, as of now, there does not seem to be any possibility of a major impact.

It, however, remains to be seen how it actually develops.

If it were to develop earlier, there could be a negative impact on the quantum and pattern of rainfall.

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