Agri Business

Records may tumble, with IMD issuing twin-cyclone alert in Arabian Sea

Vinson Kurian Thiruvananthapuram | Updated on December 05, 2019 Published on December 04, 2019

File Photo of Arabian Sea   -  The Hindu

Expect some action later this week or early next week

In a dramatic turn of events on Wednesday, the India Meteorological Department (IMD) has issued a twin-cyclone alert in the Arabian Sea for the second time during this North-East monsoon. Earlier, in October-end and early November, the literally boiling waters of the Arabian Sea had hosted Kyarr, the first supercyclone after Gonu in 2007, as well as very severe cyclone Maha concurrently for a few days.

Read | What the IMD said about Thursday's unseasonal rain in Mumbai

A similar scenario is likely emerging as South-West Arabian Sea (off Africa coast) and East-Central Arabian Sea (off Karnataka-Goa) prepare to do a repeat in December, towards the fag end of the season. International weather models suggest that the process of storm-building may not be finished yet, with the seas around Sri Lanka and adjoining Comorin likely to throw up a disturbance later this week or early next week.

The IMD said that an existing well-marked low-pressure area over Lakshadweep and adjoining South-East Arabian Sea had quickly intensified three times over to a deep depression by noon on Wednesday. This represents only a breath away from being classified as a cyclone. It was located to 600 km South-South-West of Mumbai and 490 km of West-South-West of Panjim. It may intensify into a cyclone by the same (Wednesday) evening/night but spare India's coast a direct hit since it is expected to move away to the North-Westwards (towards the open waters).

The other deep depression to the other end of the Arabian Sea basin (off Africa coast) was traced to about 650 km South-South-East of Socotra (Yemen) and 920 km East-South-East of Bosaso (Somalia). It may also intensify into a cyclone earlier in the evening. It is forecast to dig in towards the Somalia coast during the next three days.

This would go on to set up some records if we trace back history to the last four decades, said GP Sharma, President, Meteorology, at private forecaster Skymet Weather. The number seems to have exceeded the known figures during the period under reference, Sharma told BusinessLine.

The seven cyclone record

“We used to say seven cyclones in 2018 is a record, which matched with the number during the 1976 season. The brewing cyclone off the Africa coast, which is likely to be called first, becomes the eighth storm. The compatriot storm building closer home along the Karnataka-Goa coast becomes the ninth one,” he said. “I was going through the records...year 1975 too had a record of eight storms. So too year 1987. We’re still trying to search record books to find if there was a previous occasion when we have had even more. But, so far, we could lay our hands only on 1975 and 1987 with eight storms each.”

The naming of cyclones in India had started only after the supercyclone in Odisha in 1999. Before that they were referred to as the mid-September storm of Bay of Bengal or the December-end storm of Arabian Sea, or tropical storm 1, 2 or 3. The naming started in 2004 only.

Naming cyclones

Eight countries in the Indian Ocean Rim region felt the need for naming since many had turned out to be ferocious, inflicting massive damage to life and property. The first to be named was Onil in 2004 in the Arabian Sea and contributed by Bangladesh. According to Sharma, the list of names is going to exhaust soon with the latest two cyclones in the Arabian Sea.

Storms peak in May and November, during the pre- and post-monsoon seasons. And statistics show that the number of storms is more during the post-monsoon season. It is also known that the number is a little higher in the Arabian Sea than the Bay of Bengal because the former is the warmer of the two. According to Sharma, the cyclones are being triggered one after the other due to the significantly enhanced play of known oceanic parameters of El Nino (in the Equatorial Pacific) and the Indian Ocean Dipole (IOD), which refer to the differential heating of the respective oceans.

On top of this is the raised frequency of visitations by the Madden-Julian Oscillation (MJO) wave, a circum-global navigating low-pressure wave which boosts weather under its footprint. Not just this, the MJO wave is extending its stay over phases 1 (South Arabian Sea) and 2 (South Bay of Bengal), giving rise to storms.

Overstaying of ITCZ

“But the other major reason for extended storm activity this year is how the Inter-Tropical Convergence Zone (ITCZ), the global belt of rain and thunderstorms around the Equator and the main powerhouse of the monsoon, has overstayed its welcome in the region,” explained Sharma.

By December or so, the ITCZ should have shifted entirely into the Southern Hemisphere (one reason why Australia in witnessing an extended summer). But, during the last few days of November and even into the fourth day of December, the ITCZ has been active and is still hanging around to the North of the Equator. “This is unusual. With the ITCZ shifting southward, even the positive phase of the IOD (that has helped the monsoons) should have weakened. That is not the case. IOD is still holding out, though a tad low of its record peak. The MJO is still in phase one of its track. It is expected to get a move into Phase 2 sooner than later,” said Sharma.

It remains favourable for further cyclogenesis (birth of storms). That is why meteorologists suspect that another storm could be in the making around Sri Lanka and into the Comorin area before moving into the Arabian Sea. This should happen shortly, in about a week or so, said Sharma.

Global warming?

So, as mentioned earlier, oceanic parameters are playing a very significant role in cyclogenesis. As far as the Pacific is concerned, the ocean has not cooled down to below-the-threshold level. So the Pacific is warm, the Indian Ocean is warm, the IOD has been peaking this time to a record level after having started in April this year, and has maintained the above threshold levels to this day by a sufficient margin.

But this trend was discernible even before, in 1975 and 1987, as mentioned before. Why it happened then and is repeating now are topics that would need deep research. “But surely there’s no denying that temperature is on an increasing trend all over...Sydney is going through its warmest December; Perth had the warmest November after 1894. So all this is showing up at many places. So there is an indelible stamp of global warming on all these,” Sharma said.

Published on December 04, 2019
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